Re: [Intel-gfx] [PATCH] drm/i915/selftests: Confirm RING_TIMESTAMP / CTX_TIMESTAMP share a clock

[Lionel Landwerlin <lionel.g.landwerlin@intel.com>]

On 11/08/2020 12:17, Chris Wilson wrote:
> 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. As far as I can tell, this behaviour
> is undocumented.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>


I really thought the CTX_TIMESTAMP was running 8 times slower :


For the 2015 - 2016 Intel CoreTM Processors, CeleronTM Processors,
and PentiumTM Processors based on the "Skylake" Platform

Volume 2c: Command Reference: Registers
Part 1 – Registers A through L

May 2016, Revision 1.0

CTX_TIMESTAMP - Context Timestamp Count:

The granularity of this toggle is at the rate of the bit 3 in the 
"Reported Timestamp Count"
register(0x2358).. The toggle will be 8 times slower that "Reported 
Timestamp Count". The
granularity of the time stamp base unit for "Reported Timestamp Count" 
is defined in the
“Timestamp Bases” subsection in Power Management chapter.


> ---
>   drivers/gpu/drm/i915/gt/selftest_engine_pm.c | 157 +++++++++++++++++++
>   1 file changed, 157 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c
> index b08fc5390e8a..9d5778238015 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c
> @@ -5,12 +5,168 @@
>    */
>   
>   #include "i915_selftest.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"
>   
> +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 __live_engine_timestamps(struct intel_engine_cs *engine)
> +{
> +	u32 *sema = memset32(engine->status_page.addr + 1000, 0, 5);
> +	u32 offset = i915_ggtt_offset(engine->status_page.vma);
> +	struct intel_context *ce;
> +	struct i915_request *rq;
> +	u64 d_ring, d_ctx, dt;
> +	u32 *cs;
> +
> +	ce = intel_context_create(engine);
> +	if (IS_ERR(ce))
> +		return PTR_ERR(ce);
> +
> +	rq = intel_context_create_request(ce);
> +	intel_context_put(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_mono_fast_ns();
> +	write_semaphore(&sema[2], 0);
> +	udelay(100);
> +	write_semaphore(&sema[2], 1);
> +	dt = ktime_get_mono_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]\n",
> +		 engine->name, sema[1], sema[3]);
> +	pr_debug("%s RING_TIMESTAMP: [%x, %x]\n",
> +		 engine->name, sema[0], sema[4]);
> +
> +	d_ctx = sema[3] - sema[1];
> +	d_ring = sema[4] - sema[0];
> +
> +	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_ctx *= RUNTIME_INFO(engine->i915)->cs_timestamp_frequency_hz;
> +	if (IS_ICELAKE(engine->i915))
> +		d_ring *= 12500000; /* Fixed 80ns for icl ctx timestamp? */
> +	else
> +		d_ring *= RUNTIME_INFO(engine->i915)->cs_timestamp_frequency_hz;
> +
> +	if (4 * d_ctx > 5 * d_ring || 5 * d_ctx < 4 * 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;
> @@ -177,6 +333,7 @@ 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),
>   	};


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