Chris Wilson <ch...@chris-wilson.co.uk> writes:
> We assume that both timestamps are driven off the same clock [reported
> to userspace as I915_PARAM_CS_TIMESTAMP_FREQUENCY]. Verify that this is
> so by reading the timestamp registers around a busywait (on an otherwise
> idle engine so there should be no preemptions).
>
> v2: Icelake (not ehl, nor tgl) seems to be using a fixed 80ns interval
> for, and only for, CTX_TIMESTAMP -- or it may be GPU frequency and the
> test is always running at maximum frequency?. As far as I can tell, this
> isolated change in behaviour is undocumented.
>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuopp...@linux.intel.com>
> ---
> drivers/gpu/drm/i915/gt/selftest_engine_pm.c | 203 ++++++++++++++++++-
> 1 file changed, 202 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c
> b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c
> index 163a10b07f85..d88504a5d69c 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c
> @@ -4,15 +4,215 @@
> * Copyright © 2018 Intel Corporation
> */
>
> -#include "intel_gpu_commands.h"
> +#include <linux/sort.h>
>
> #include "i915_selftest.h"
> +#include "intel_gpu_commands.h"
> +#include "intel_gt_clock_utils.h"
> #include "selftest_engine.h"
> #include "selftest_engine_heartbeat.h"
> #include "selftests/igt_atomic.h"
> #include "selftests/igt_flush_test.h"
> #include "selftests/igt_spinner.h"
>
> +#define COUNT 5
> +
> +static int cmp_u64(const void *A, const void *B)
> +{
> + const u64 *a = A, *b = B;
> +
> + return *a - *b;
> +}
> +
> +static u64 trifilter(u64 *a)
> +{
> + sort(a, COUNT, sizeof(*a), cmp_u64, NULL);
> + return (a[1] + 2 * a[2] + a[3]) >> 2;
> +}
> +
> +static u32 *emit_wait(u32 *cs, u32 offset, int op, u32 value)
> +{
> + *cs++ = MI_SEMAPHORE_WAIT |
> + MI_SEMAPHORE_GLOBAL_GTT |
> + MI_SEMAPHORE_POLL |
> + op;
> + *cs++ = value;
> + *cs++ = offset;
> + *cs++ = 0;
> +
> + return cs;
> +}
> +
> +static u32 *emit_store(u32 *cs, u32 offset, u32 value)
> +{
> + *cs++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
> + *cs++ = offset;
> + *cs++ = 0;
> + *cs++ = value;
> +
> + return cs;
> +}
> +
> +static u32 *emit_srm(u32 *cs, i915_reg_t reg, u32 offset)
> +{
> + *cs++ = MI_STORE_REGISTER_MEM_GEN8 | MI_USE_GGTT;
> + *cs++ = i915_mmio_reg_offset(reg);
> + *cs++ = offset;
> + *cs++ = 0;
> +
> + return cs;
> +}
> +
> +static void write_semaphore(u32 *x, u32 value)
> +{
> + WRITE_ONCE(*x, value);
> + wmb();
> +}
> +
> +static int __measure_timestamps(struct intel_context *ce,
> + u64 *dt, u64 *d_ring, u64 *d_ctx)
> +{
> + struct intel_engine_cs *engine = ce->engine;
> + u32 *sema = memset32(engine->status_page.addr + 1000, 0, 5);
> + u32 offset = i915_ggtt_offset(engine->status_page.vma);
> + struct i915_request *rq;
> + u32 *cs;
> +
> + rq = intel_context_create_request(ce);
> + if (IS_ERR(rq))
> + return PTR_ERR(rq);
> +
> + cs = intel_ring_begin(rq, 28);
> + if (IS_ERR(cs)) {
> + i915_request_add(rq);
> + return PTR_ERR(cs);
> + }
> +
> + /* Signal & wait for start */
> + cs = emit_store(cs, offset + 4008, 1);
> + cs = emit_wait(cs, offset + 4008, MI_SEMAPHORE_SAD_NEQ_SDD, 1);
> +
> + cs = emit_srm(cs, RING_TIMESTAMP(engine->mmio_base), offset + 4000);
> + cs = emit_srm(cs, RING_CTX_TIMESTAMP(engine->mmio_base), offset + 4004);
> +
> + /* Busy wait */
> + cs = emit_wait(cs, offset + 4008, MI_SEMAPHORE_SAD_EQ_SDD, 1);
> +
> + cs = emit_srm(cs, RING_TIMESTAMP(engine->mmio_base), offset + 4016);
> + cs = emit_srm(cs, RING_CTX_TIMESTAMP(engine->mmio_base), offset + 4012);
> +
> + intel_ring_advance(rq, cs);
> + i915_request_get(rq);
> + i915_request_add(rq);
> + intel_engine_flush_submission(engine);
> +
> + /* Wait for the request to start executing, that then waits for us */
> + while (READ_ONCE(sema[2]) == 0)
> + cpu_relax();
> +
> + /* Run the request for a 100us, sampling timestamps before/after */
> + preempt_disable();
> + *dt = ktime_get_raw_fast_ns();
> + write_semaphore(&sema[2], 0);
> + udelay(100);
> + write_semaphore(&sema[2], 1);
> + *dt = ktime_get_raw_fast_ns() - *dt;
> + preempt_enable();
> +
> + if (i915_request_wait(rq, 0, HZ / 2) < 0) {
> + i915_request_put(rq);
> + return -ETIME;
> + }
> + i915_request_put(rq);
> +
> + pr_debug("%s CTX_TIMESTAMP: [%x, %x], RING_TIMESTAMP: [%x, %x]\n",
> + engine->name, sema[1], sema[3], sema[0], sema[4]);
> +
> + *d_ctx = sema[3] - sema[1];
> + *d_ring = sema[4] - sema[0];
> + return 0;
> +}
> +
> +static int __live_engine_timestamps(struct intel_engine_cs *engine)
> +{
> + u64 s_ring[COUNT], s_ctx[COUNT], st[COUNT], d_ring, d_ctx, dt;
> + struct intel_context *ce;
> + int i, err = 0;
> +
> + ce = intel_context_create(engine);
> + if (IS_ERR(ce))
> + return PTR_ERR(ce);
> +
> + for (i = 0; i < COUNT; i++) {
> + err = __measure_timestamps(ce, &st[i], &s_ring[i], &s_ctx[i]);
> + if (err)
> + break;
> + }
> + intel_context_put(ce);
> + if (err)
> + return err;
> +
> + dt = trifilter(st);
> + d_ring = trifilter(s_ring);
> + d_ctx = trifilter(s_ctx);
> +
> + pr_info("%s elapsed:%lldns, CTX_TIMESTAMP:%dns, RING_TIMESTAMP:%dns\n",
> + engine->name, dt,
> + intel_gt_clock_interval_to_ns(engine->gt, d_ctx),
> + intel_gt_clock_interval_to_ns(engine->gt, d_ring));
> +
> + d_ring = intel_gt_clock_interval_to_ns(engine->gt, d_ring);
> + if (3 * dt > 4 * d_ring || 4 * dt < 3 * d_ring) {
> + pr_err("%s Mismatch between ring timestamp and walltime!\n",
> + engine->name);
> + return -EINVAL;
> + }
> +
> + d_ring = trifilter(s_ring);
> + d_ctx = trifilter(s_ctx);
> +
> + d_ctx *= RUNTIME_INFO(engine->i915)->cs_timestamp_frequency_hz;
> + if (IS_ICELAKE(engine->i915))
> + d_ring *= 12500000; /* Fixed 80ns for icl ctx timestamp? */
This is...weird. But I am not going to argue against hardware.
Will be interesting to see if this can find something funny.
Reviewed-by: Mika Kuoppala <mika.kuopp...@linux.intel.com>
> + else
> + d_ring *= RUNTIME_INFO(engine->i915)->cs_timestamp_frequency_hz;
> +
> + if (3 * d_ctx > 4 * d_ring || 4 * d_ctx < 3 * d_ring) {
> + pr_err("%s Mismatch between ring and context timestamps!\n",
> + engine->name);
> + return -EINVAL;
> + }
> +
> + return 0;
> +}
> +
> +static int live_engine_timestamps(void *arg)
> +{
> + struct intel_gt *gt = arg;
> + struct intel_engine_cs *engine;
> + enum intel_engine_id id;
> +
> + /*
> + * Check that CS_TIMESTAMP / CTX_TIMESTAMP are in sync, i.e. share
> + * the same CS clock.
> + */
> +
> + if (INTEL_GEN(gt->i915) < 8)
> + return 0;
> +
> + for_each_engine(engine, gt, id) {
> + int err;
> +
> + st_engine_heartbeat_disable(engine);
> + err = __live_engine_timestamps(engine);
> + st_engine_heartbeat_enable(engine);
> + if (err)
> + return err;
> + }
> +
> + return 0;
> +}
> +
> static int live_engine_busy_stats(void *arg)
> {
> struct intel_gt *gt = arg;
> @@ -179,6 +379,7 @@ static int live_engine_pm(void *arg)
> int live_engine_pm_selftests(struct intel_gt *gt)
> {
> static const struct i915_subtest tests[] = {
> + SUBTEST(live_engine_timestamps),
> SUBTEST(live_engine_busy_stats),
> SUBTEST(live_engine_pm),
> };
> --
> 2.20.1
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