Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx> writes:
> The CSB format has been reworked for Gen12 to include information on
> both the context we're switching away from and the context we're
> switching to. After the change, some of the events don't have their
> own bit anymore and need to be inferred from other values in the csb.
> One of the context IDs (0x7FF) has also been reserved to indicate
> the invalid ctx, i.e. engine idle.
>
> Note that the full context ID includes the SW counter as well, but since
> we currently only care if the context is valid or not we can ignore that
> part.
>
> v2: fix mask size, fix and expand comments (Tvrtko),
> use if-ladder (Chris)
>
> Bspec: 45555, 46144
> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gt/intel_lrc.c | 79 ++++++++++++++++++++++++++++-
> 1 file changed, 78 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 48b7114094f1..6cd756b15098 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -163,6 +163,13 @@
>
> #define CTX_DESC_FORCE_RESTORE BIT_ULL(2)
>
> +#define GEN12_CTX_STATUS_SWITCHED_TO_NEW_QUEUE (0x1) /* lower csb dword */
> +#define GEN12_CTX_SWITCH_DETAIL(csb_dw) ((csb_dw) & 0xF) /* upper csb dword */
> +#define GEN12_CSB_SW_CTX_ID_MASK GENMASK(25, 15)
> +#define GEN12_IDLE_CTX_ID 0x7FF
Without looking at bspec first I thought FIELD_GET(GEN12_CSB_SW_CTX_ID_MASK, ~0)
would emphasize the mask size. But as bspec uses 0x7FF it is well suited
in here too.
> +#define GEN12_CSB_CTX_VALID(csb_dw) \
> + (FIELD_GET(GEN12_CSB_SW_CTX_ID_MASK, csb_dw) != GEN12_IDLE_CTX_ID)
> +
> /* Typical size of the average request (2 pipecontrols and a MI_BB) */
> #define EXECLISTS_REQUEST_SIZE 64 /* bytes */
> #define WA_TAIL_DWORDS 2
> @@ -1326,6 +1333,69 @@ enum csb_step {
> CSB_COMPLETE,
> };
>
> +/*
> + * Starting with Gen12, the status has a new format:
> + *
> + * bit 0: switched to new queue
> + * bit 1: reserved
> + * bit 2: semaphore wait mode (poll or signal), only valid when
> + * switch detail is set to "wait on semaphore"
> + * bits 3-5: engine class
> + * bits 6-11: engine instance
> + * bits 12-14: reserved
> + * bits 15-25: sw context id of the lrc the GT switched to
> + * bits 26-31: sw counter of the lrc the GT switched to
> + * bits 32-35: context switch detail
> + * - 0: ctx complete
> + * - 1: wait on sync flip
> + * - 2: wait on vblank
> + * - 3: wait on scanline
> + * - 4: wait on semaphore
> + * - 5: context preempted (not on SEMAPHORE_WAIT or
> + * WAIT_FOR_EVENT)
> + * bit 36: reserved
> + * bits 37-43: wait detail (for switch detail 1 to 4)
> + * bits 44-46: reserved
> + * bits 47-57: sw context id of the lrc the GT switched away from
> + * bits 58-63: sw counter of the lrc the GT switched away from
> + */
> +static inline enum csb_step
> +gen12_csb_parse(const struct intel_engine_execlists *execlists, const u32 *csb)
> +{
> + u32 lower_dw = csb[0];
> + u32 upper_dw = csb[1];
> + bool ctx_to_valid = GEN12_CSB_CTX_VALID(lower_dw);
> + bool ctx_away_valid = GEN12_CSB_CTX_VALID(upper_dw);
> + bool new_queue = lower_dw & GEN12_CTX_STATUS_SWITCHED_TO_NEW_QUEUE;
> +
For a longer more complex function, the above could be consts to
relieve the readers burden. In here, terse is as good.
> + if (!ctx_away_valid && ctx_to_valid)
> + return CSB_PROMOTE;
> +
> + /*
> + * The context switch detail is not guaranteed to be 5 when a preemption
> + * occurs, so we can't just check for that. The check below works for
> + * all the cases we care about, including preemptions of WAIT
> + * instructions and lite-restore. Preempt-to-idle via the CTRL register
> + * would require some extra handling, but we don't support that.
> + */
> + if (new_queue && ctx_away_valid)
> + return CSB_PREEMPT;
> +
> + /*
> + * switch detail = 5 is covered by the case above and we do not expect a
> + * context switch on an unsuccessful wait instruction since we always
> + * use polling mode.
> + */
> + GEM_BUG_ON(GEN12_CTX_SWITCH_DETAIL(upper_dw));
> +
> + if (*execlists->active) {
> + GEM_BUG_ON(!ctx_away_valid);
> + return CSB_COMPLETE;
> + }
> +
> + return CSB_NOP;
I don't have a tgl to play with to try it out, but the comments are golden.
> +}
> +
> static inline enum csb_step
> csb_parse(const struct intel_engine_execlists *execlists, const u32 *csb)
> {
> @@ -1380,6 +1450,8 @@ static void process_csb(struct intel_engine_cs *engine)
> rmb();
>
> do {
> + enum csb_step csb_step;
> +
> if (++head == num_entries)
> head = 0;
>
> @@ -1405,7 +1477,12 @@ static void process_csb(struct intel_engine_cs *engine)
> engine->name, head,
> buf[2 * head + 0], buf[2 * head + 1]);
>
> - switch (csb_parse(execlists, buf + 2 * head)) {
> + if (INTEL_GEN(engine->i915) >= 12)
> + csb_step = gen12_csb_parse(execlists, buf + 2 * head);
> + else
> + csb_step = csb_parse(execlists, buf + 2 * head);
This could have been s/csb_parse/gen8_csb_parse to emphasize the
gen range but I am not insisting.
I remember doing a patch where we read full 64bit at a time,
as we use upper part in tracing as well on gen < 12.
Could be that Chris didn't like it. But now with doing a csb
parsing function pointer for each gen range, it could fly.
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> +
> + switch (csb_step) {
> case CSB_PREEMPT: /* cancel old inflight, prepare for switch */
> trace_ports(execlists, "preempted", execlists->active);
>
> --
> 2.22.0
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