On Tue, 24 Mar 2020 11:54:55 -0700, Umesh Nerlige Ramappa wrote: > > From: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx> > > We're about to introduce an options to open the perf stream, giving > the user ability to configure how often it wants the kernel to poll > the OA registers for available data. > > Right now the workaround against the OA tail pointer race condition > requires at least twice the internal kernel polling timer to make any > data available. > > This changes introduce checks on the OA data written into the circular > buffer to make as much data as possible available on the first > iteration of the polling timer. Reviewed-by: Ashutosh Dixit <ashutosh.dixit@xxxxxxxxx> > > v2: Use OA_TAKEN macro without the gtt_offset (Lionel) > v3: (Umesh) > - Rebase > - Change report to report32 from below review > https://patchwork.freedesktop.org/patch/330704/?series=66697&rev=1 > v4: (Ashutosh, Lionel) > - Fix checkpatch errors > - Fix aging_timestamp initialization > - Check for only one valid landed report > - Fix check for unlanded report > v5: (Ashutosh) > - Fix bug in accurately determining landed report. > - Optimize the check for landed reports by going as far as the > previously determined aged tail. > > Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx> > Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx> > --- > drivers/gpu/drm/i915/i915_perf.c | 204 ++++++++++--------------- > drivers/gpu/drm/i915/i915_perf_types.h | 28 ++-- > 2 files changed, 97 insertions(+), 135 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c > index 3222f6cd8255..4583ae9b77be 100644 > --- a/drivers/gpu/drm/i915/i915_perf.c > +++ b/drivers/gpu/drm/i915/i915_perf.c > @@ -223,26 +223,17 @@ > * > * Although this can be observed explicitly while copying reports to userspace > * by checking for a zeroed report-id field in tail reports, we want to account > - * for this earlier, as part of the oa_buffer_check to avoid lots of redundant > - * read() attempts. > - * > - * In effect we define a tail pointer for reading that lags the real tail > - * pointer by at least %OA_TAIL_MARGIN_NSEC nanoseconds, which gives enough > - * time for the corresponding reports to become visible to the CPU. > - * > - * To manage this we actually track two tail pointers: > - * 1) An 'aging' tail with an associated timestamp that is tracked until we > - * can trust the corresponding data is visible to the CPU; at which point > - * it is considered 'aged'. > - * 2) An 'aged' tail that can be used for read()ing. > - * > - * The two separate pointers let us decouple read()s from tail pointer aging. > - * > - * The tail pointers are checked and updated at a limited rate within a hrtimer > - * callback (the same callback that is used for delivering EPOLLIN events) > - * > - * Initially the tails are marked invalid with %INVALID_TAIL_PTR which > - * indicates that an updated tail pointer is needed. > + * for this earlier, as part of the oa_buffer_check_unlocked to avoid lots of > + * redundant read() attempts. > + * > + * We workaround this issue in oa_buffer_check_unlocked() by reading the reports > + * in the OA buffer, starting from the tail reported by the HW until we find a > + * report with its first 2 dwords not 0 meaning its previous report is > + * completely in memory and ready to be read. Those dwords are also set to 0 > + * once read and the whole buffer is cleared upon OA buffer initialization. The > + * first dword is the reason for this report while the second is the timestamp, > + * making the chances of having those 2 fields at 0 fairly unlikely. A more > + * detailed explanation is available in oa_buffer_check_unlocked(). > * > * Most of the implementation details for this workaround are in > * oa_buffer_check_unlocked() and _append_oa_reports() > @@ -454,8 +445,8 @@ static u32 gen7_oa_hw_tail_read(struct i915_perf_stream *stream) > * (See description of OA_TAIL_MARGIN_NSEC above for further details.) > * > * Besides returning true when there is data available to read() this function > - * also has the side effect of updating the oa_buffer.tails[], .aging_timestamp > - * and .aged_tail_idx state used for reading. > + * also updates the tail, aging_tail and aging_timestamp in the oa_buffer > + * object. > * > * Note: It's safe to read OA config state here unlocked, assuming that this is > * only called while the stream is enabled, while the global OA configuration > @@ -465,28 +456,18 @@ static u32 gen7_oa_hw_tail_read(struct i915_perf_stream *stream) > */ > static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream) > { > + u32 gtt_offset = i915_ggtt_offset(stream->oa_buffer.vma); > int report_size = stream->oa_buffer.format_size; > unsigned long flags; > - unsigned int aged_idx; > - u32 head, hw_tail, aged_tail, aging_tail; > + u32 hw_tail; > u64 now; > > /* We have to consider the (unlikely) possibility that read() errors > - * could result in an OA buffer reset which might reset the head, > - * tails[] and aged_tail state. > + * could result in an OA buffer reset which might reset the head and > + * tail state. > */ > spin_lock_irqsave(&stream->oa_buffer.ptr_lock, flags); > > - /* NB: The head we observe here might effectively be a little out of > - * date (between head and tails[aged_idx].offset if there is currently > - * a read() in progress. > - */ > - head = stream->oa_buffer.head; > - > - aged_idx = stream->oa_buffer.aged_tail_idx; > - aged_tail = stream->oa_buffer.tails[aged_idx].offset; > - aging_tail = stream->oa_buffer.tails[!aged_idx].offset; > - > hw_tail = stream->perf->ops.oa_hw_tail_read(stream); > > /* The tail pointer increases in 64 byte increments, > @@ -496,64 +477,61 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream) > > now = ktime_get_mono_fast_ns(); > > - /* Update the aged tail > - * > - * Flip the tail pointer available for read()s once the aging tail is > - * old enough to trust that the corresponding data will be visible to > - * the CPU... > - * > - * Do this before updating the aging pointer in case we may be able to > - * immediately start aging a new pointer too (if new data has become > - * available) without needing to wait for a later hrtimer callback. > - */ > - if (aging_tail != INVALID_TAIL_PTR && > - ((now - stream->oa_buffer.aging_timestamp) > > - OA_TAIL_MARGIN_NSEC)) { > - > - aged_idx ^= 1; > - stream->oa_buffer.aged_tail_idx = aged_idx; > + if (hw_tail == stream->oa_buffer.aging_tail && > + (now - stream->oa_buffer.aging_timestamp) > OA_TAIL_MARGIN_NSEC) { > + /* If the HW tail hasn't move since the last check and the HW > + * tail has been aging for long enough, declare it the new > + * tail. > + */ > + stream->oa_buffer.tail = stream->oa_buffer.aging_tail; > + } else { > + u32 head, tail, aged_tail; > > - aged_tail = aging_tail; > + /* NB: The head we observe here might effectively be a little > + * out of date. If a read() is in progress, the head could be > + * anywhere between this head and stream->oa_buffer.tail. > + */ > + head = stream->oa_buffer.head - gtt_offset; > + aged_tail = stream->oa_buffer.tail - gtt_offset; > + > + hw_tail -= gtt_offset; > + tail = hw_tail; > + > + /* Walk the stream backward until we find a report with dword 0 > + * & 1 not at 0. Since the circular buffer pointers progress by > + * increments of 64 bytes and that reports can be up to 256 > + * bytes long, we can't tell whether a report has fully landed > + * in memory before the first 2 dwords of the following report > + * have effectively landed. > + * > + * This is assuming that the writes of the OA unit land in > + * memory in the order they were written to. > + * If not : (╯°□°）╯︵ ┻━┻ > + */ > + while (OA_TAKEN(tail, aged_tail) >= report_size) { > + u32 *report32 = (void *)(stream->oa_buffer.vaddr + tail); > > - /* Mark that we need a new pointer to start aging... */ > - stream->oa_buffer.tails[!aged_idx].offset = INVALID_TAIL_PTR; > - aging_tail = INVALID_TAIL_PTR; > - } > + if (report32[0] != 0 || report32[1] != 0) > + break; > > - /* Update the aging tail > - * > - * We throttle aging tail updates until we have a new tail that > - * represents >= one report more data than is already available for > - * reading. This ensures there will be enough data for a successful > - * read once this new pointer has aged and ensures we will give the new > - * pointer time to age. > - */ > - if (aging_tail == INVALID_TAIL_PTR && > - (aged_tail == INVALID_TAIL_PTR || > - OA_TAKEN(hw_tail, aged_tail) >= report_size)) { > - struct i915_vma *vma = stream->oa_buffer.vma; > - u32 gtt_offset = i915_ggtt_offset(vma); > - > - /* Be paranoid and do a bounds check on the pointer read back > - * from hardware, just in case some spurious hardware condition > - * could put the tail out of bounds... > - */ > - if (hw_tail >= gtt_offset && > - hw_tail < (gtt_offset + OA_BUFFER_SIZE)) { > - stream->oa_buffer.tails[!aged_idx].offset = > - aging_tail = hw_tail; > - stream->oa_buffer.aging_timestamp = now; > - } else { > - drm_err(&stream->perf->i915->drm, > - "Ignoring spurious out of range OA buffer tail pointer = %x\n", > - hw_tail); > + tail = (tail - report_size) & (OA_BUFFER_SIZE - 1); > } > + > + if (OA_TAKEN(hw_tail, tail) > report_size && > + __ratelimit(&stream->perf->tail_pointer_race)) > + DRM_NOTE("unlanded report(s) head=0x%x " > + "tail=0x%x hw_tail=0x%x\n", > + head, tail, hw_tail); > + > + stream->oa_buffer.tail = gtt_offset + tail; > + stream->oa_buffer.aging_tail = gtt_offset + hw_tail; > + stream->oa_buffer.aging_timestamp = now; > } > > spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags); > > - return aged_tail == INVALID_TAIL_PTR ? > - false : OA_TAKEN(aged_tail, head) >= report_size; > + return OA_TAKEN(stream->oa_buffer.tail - gtt_offset, > + stream->oa_buffer.head - gtt_offset) >= report_size; > } > > /** > @@ -671,7 +649,6 @@ static int gen8_append_oa_reports(struct i915_perf_stream *stream, > u32 mask = (OA_BUFFER_SIZE - 1); > size_t start_offset = *offset; > unsigned long flags; > - unsigned int aged_tail_idx; > u32 head, tail; > u32 taken; > int ret = 0; > @@ -682,18 +659,10 @@ static int gen8_append_oa_reports(struct i915_perf_stream *stream, > spin_lock_irqsave(&stream->oa_buffer.ptr_lock, flags); > > head = stream->oa_buffer.head; > - aged_tail_idx = stream->oa_buffer.aged_tail_idx; > - tail = stream->oa_buffer.tails[aged_tail_idx].offset; > + tail = stream->oa_buffer.tail; > > spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags); > > - /* > - * An invalid tail pointer here means we're still waiting for the poll > - * hrtimer callback to give us a pointer > - */ > - if (tail == INVALID_TAIL_PTR) > - return -EAGAIN; > - > /* > * NB: oa_buffer.head/tail include the gtt_offset which we don't want > * while indexing relative to oa_buf_base. > @@ -827,13 +796,11 @@ static int gen8_append_oa_reports(struct i915_perf_stream *stream, > } > > /* > - * The above reason field sanity check is based on > - * the assumption that the OA buffer is initially > - * zeroed and we reset the field after copying so the > - * check is still meaningful once old reports start > - * being overwritten. > + * Clear out the first 2 dword as a mean to detect unlanded > + * reports. > */ > report32[0] = 0; > + report32[1] = 0; > } > > if (start_offset != *offset) { > @@ -974,7 +941,6 @@ static int gen7_append_oa_reports(struct i915_perf_stream *stream, > u32 mask = (OA_BUFFER_SIZE - 1); > size_t start_offset = *offset; > unsigned long flags; > - unsigned int aged_tail_idx; > u32 head, tail; > u32 taken; > int ret = 0; > @@ -985,17 +951,10 @@ static int gen7_append_oa_reports(struct i915_perf_stream *stream, > spin_lock_irqsave(&stream->oa_buffer.ptr_lock, flags); > > head = stream->oa_buffer.head; > - aged_tail_idx = stream->oa_buffer.aged_tail_idx; > - tail = stream->oa_buffer.tails[aged_tail_idx].offset; > + tail = stream->oa_buffer.tail; > > spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags); > > - /* An invalid tail pointer here means we're still waiting for the poll > - * hrtimer callback to give us a pointer > - */ > - if (tail == INVALID_TAIL_PTR) > - return -EAGAIN; > - > /* NB: oa_buffer.head/tail include the gtt_offset which we don't want > * while indexing relative to oa_buf_base. > */ > @@ -1053,13 +1012,11 @@ static int gen7_append_oa_reports(struct i915_perf_stream *stream, > if (ret) > break; > > - /* The above report-id field sanity check is based on > - * the assumption that the OA buffer is initially > - * zeroed and we reset the field after copying so the > - * check is still meaningful once old reports start > - * being overwritten. > + /* Clear out the first 2 dwords as a mean to detect unlanded > + * reports. > */ > report32[0] = 0; > + report32[1] = 0; > } > > if (start_offset != *offset) { > @@ -1438,8 +1395,8 @@ static void gen7_init_oa_buffer(struct i915_perf_stream *stream) > gtt_offset | OABUFFER_SIZE_16M); > > /* Mark that we need updated tail pointers to read from... */ > - stream->oa_buffer.tails[0].offset = INVALID_TAIL_PTR; > - stream->oa_buffer.tails[1].offset = INVALID_TAIL_PTR; > + stream->oa_buffer.aging_tail = INVALID_TAIL_PTR; > + stream->oa_buffer.tail = gtt_offset; > > spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags); > > @@ -1492,8 +1449,8 @@ static void gen8_init_oa_buffer(struct i915_perf_stream *stream) > intel_uncore_write(uncore, GEN8_OATAILPTR, gtt_offset & GEN8_OATAILPTR_MASK); > > /* Mark that we need updated tail pointers to read from... */ > - stream->oa_buffer.tails[0].offset = INVALID_TAIL_PTR; > - stream->oa_buffer.tails[1].offset = INVALID_TAIL_PTR; > + stream->oa_buffer.aging_tail = INVALID_TAIL_PTR; > + stream->oa_buffer.tail = gtt_offset; > > /* > * Reset state used to recognise context switches, affecting which > @@ -1548,8 +1505,8 @@ static void gen12_init_oa_buffer(struct i915_perf_stream *stream) > gtt_offset & GEN12_OAG_OATAILPTR_MASK); > > /* Mark that we need updated tail pointers to read from... */ > - stream->oa_buffer.tails[0].offset = INVALID_TAIL_PTR; > - stream->oa_buffer.tails[1].offset = INVALID_TAIL_PTR; > + stream->oa_buffer.aging_tail = INVALID_TAIL_PTR; > + stream->oa_buffer.tail = gtt_offset; > > /* > * Reset state used to recognise context switches, affecting which > @@ -4398,6 +4355,11 @@ void i915_perf_init(struct drm_i915_private *i915) > ratelimit_set_flags(&perf->spurious_report_rs, > RATELIMIT_MSG_ON_RELEASE); > > + ratelimit_state_init(&perf->tail_pointer_race, > + 5 * HZ, 10); > + ratelimit_set_flags(&perf->tail_pointer_race, > + RATELIMIT_MSG_ON_RELEASE); > + > atomic64_set(&perf->noa_programming_delay, > 500 * 1000 /* 500us */); > > diff --git a/drivers/gpu/drm/i915/i915_perf_types.h b/drivers/gpu/drm/i915/i915_perf_types.h > index 32289cbda648..c3ab184c604a 100644 > --- a/drivers/gpu/drm/i915/i915_perf_types.h > +++ b/drivers/gpu/drm/i915/i915_perf_types.h > @@ -273,21 +273,10 @@ struct i915_perf_stream { > spinlock_t ptr_lock; > > /** > - * @tails: One 'aging' tail pointer and one 'aged' tail pointer ready to > - * used for reading. > - * > - * Initial values of 0xffffffff are invalid and imply that an > - * update is required (and should be ignored by an attempted > - * read) > + * @aging_tail: The last HW tail reported by HW. The data > + * might not have made it to memory yet though. > */ > - struct { > - u32 offset; > - } tails[2]; > - > - /** > - * @aged_tail_idx: Index for the aged tail ready to read() data up to. > - */ > - unsigned int aged_tail_idx; > + u32 aging_tail; > > /** > * @aging_timestamp: A monotonic timestamp for when the current aging tail pointer > @@ -303,6 +292,11 @@ struct i915_perf_stream { > * OA buffer data to userspace. > */ > u32 head; > + > + /** > + * @tail: The last verified tail that can be read by userspace. > + */ > + u32 tail; > } oa_buffer; > > /** > @@ -420,6 +414,12 @@ struct i915_perf { > */ > struct ratelimit_state spurious_report_rs; > > + /** > + * For rate limiting any notifications of tail pointer > + * race. > + */ > + struct ratelimit_state tail_pointer_race; > + > u32 gen7_latched_oastatus1; > u32 ctx_oactxctrl_offset; > u32 ctx_flexeu0_offset; > -- > 2.20.1 > _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
