On Tue, Feb 21, 2023 at 10:51:57AM -0800, Dixit, Ashutosh wrote:
On Fri, 17 Feb 2023 17:57:02 -0800, Dixit, Ashutosh wrote:
On Fri, 17 Feb 2023 16:05:50 -0800, Umesh Nerlige Ramappa wrote:
> On Fri, Feb 17, 2023 at 12:58:18PM -0800, Dixit, Ashutosh wrote:
> > On Thu, 16 Feb 2023 16:58:48 -0800, Umesh Nerlige Ramappa wrote:
> >>
> >
> > Hi Umesh, couple of nits below.
> >
> >> Some of the newer OA formats are not powers of 2. For those formats,
> >> adjust the hw_tail accordingly when checking for new reports.
> >>
> >> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx>
> >> ---
> >> drivers/gpu/drm/i915/i915_perf.c | 50 ++++++++++++++++++--------------
> >> 1 file changed, 28 insertions(+), 22 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> >> index 9715b964aa1e..d3a1892c93be 100644
> >> --- a/drivers/gpu/drm/i915/i915_perf.c
> >> +++ b/drivers/gpu/drm/i915/i915_perf.c
> >> @@ -542,6 +542,7 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream)
> >> bool pollin;
> >> u32 hw_tail;
> >> u64 now;
> >> + u32 partial_report_size;
> >>
> >> /* We have to consider the (unlikely) possibility that read() errors
> >> * could result in an OA buffer reset which might reset the head and
> >> @@ -551,10 +552,16 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream)
> >>
> >> hw_tail = stream->perf->ops.oa_hw_tail_read(stream);
> >>
> >> - /* The tail pointer increases in 64 byte increments,
> >> - * not in report_size steps...
> >> + /* The tail pointer increases in 64 byte increments, whereas report
> >> + * sizes need not be integral multiples or 64 or powers of 2.
> > s/or/of/ ---------------------------------------^
> >
> > Also I think report sizes can only be multiples of 64, the ones we have
> > seen till now definitely are. Also the lower 6 bits of tail pointer are 0.
>
> Agree, the only addition to the old comment should be that the new reports
> may not be powers of 2.
>
> >
> >> + * Compute potentially partially landed report in the OA buffer
> >> */
> >> - hw_tail &= ~(report_size - 1);
> >> + partial_report_size = OA_TAKEN(hw_tail, stream->oa_buffer.tail);
> >> + partial_report_size %= report_size;
> >> +
> >> + /* Subtract partial amount off the tail */
> >> + hw_tail = gtt_offset + ((hw_tail - partial_report_size) &
> >> + (stream->oa_buffer.vma->size - 1));
> >
> > Couple of questions here because OA_TAKEN uses OA_BUFFER_SIZE and the above
> > expression uses stream->oa_buffer.vma->size:
> >
> > 1. Is 'OA_BUFFER_SIZE == stream->oa_buffer.vma->size'? We seem to be using
> > the two interchaneably in the code.
>
> Yes. I think the code was updated to use vma->size when support for
> selecting OA buffer size along with large OA buffers was added, but we
> haven't pushed that upstream yet. Since I have cherry-picked patches here,
> there is some inconsistency. I would just change this patch to use
> OA_BUFFER_SIZE for now.
>
> > 2. If yes, can we add an assert about this in alloc_oa_buffer?
>
> If I change to OA_BUFFER_SIZE, then okay to skip assert?
Yes.
> Do you suspect that the vma size may actually differ from what we
> requested?
Not sure how shmem objects are allocated but my guess would be that for a
nice whole size like 16 M they the vma size will be the same. So ok to just
use OA_BUFFER_SIZE in a couple of places in this patch and skip the
assert. As long as vma_size >= OA_BUFFER_SIZE we are ok.
>
> > 3. Can the above expression be changed to:
> >
> > hw_tail = gtt_offset + OA_TAKEN(hw_tail, partial_report_size);
>
> Not if hw_tail has rolled over, but stream->oa_buffer.tail hasn't.
Why not, the two expressions are exactly the same? And anyway
stream->oa_buffer.tail is already handled in the first OA_TAKEN expression.
Basically, for me OA_TAKEN is a "circular diff" (for a power-of-2 sized
circular buffer), so anywhere we have these "circular diff" opereations we
should be able to replace them by OA_TAKEN.
I guess I misread your comment. They are indeed identical. I can change
that.
Thanks,
Umesh
