Re: [RFC v3 00/11] i915 PMU and engine busy stats

Rogozhkin, Dmitry V
2017-09-12T02:03:07Z

Hi,

Just tried v3 series. perf-stat works fine. From the IGT tests which I wrote for i915 PMU
(https://patchwork.freedesktop.org/series/29313/) all pass (assuming pmu.enabled will be exposed
in debugfs) except cpu_online subtest. And this is pretty interesting - see details below.

Ok, be prepared for the long mail:)...

So, cpu_online subtest loads RCS0 engine 100% and starts to put CPUs offline one by one starting
from CPU0 (don't forget to have CONFIG_BOOTPARAM_HOTPLUG_CPU0=y in .config). Test expectation is
that i915 PMU will report almost 100% (with 2% tolerance) busyness of RCS0. Test requests metric
just twice: before running on RCS0 and right after. This fails as follows:

Executed on rcs0 for 32004262184us
i915/rcs0-busy/: 2225723999us
(perf_pmu:6325) CRITICAL: Test assertion failure function test_cpu_online, file perf_pmu.c:719:
(perf_pmu:6325) CRITICAL: Failed assertion: perf_elapsed(&pm.metrics[0]) > (1-USAGE_TOLERANCE) * elapsed_ns(&start, &now)
Stack trace:
#0 [__igt_fail_assert+0xf1]
#1 [__real_main773+0xff1]
#2 [main+0x35]
#3 [__libc_start_main+0xf5]
#4 [_start+0x29]
#5 [<unknown>+0x29]
Subtest cpu_online failed.
**** DEBUG ****
(perf_pmu:6325) DEBUG: Test requirement passed: is_hotplug_cpu0()
(perf_pmu:6325) INFO: perf_init: enabled 1 metrics from 1 requested
(perf_pmu:6325) ioctl-wrappers-DEBUG: Test requirement passed: gem_has_ring(fd, ring)
(perf_pmu:6325) INFO: Executed on rcs0 for 32004262184us
(perf_pmu:6325) INFO: i915/rcs0-busy/: 2225723999us
(perf_pmu:6325) CRITICAL: Test assertion failure function test_cpu_online, file perf_pmu.c:719:
(perf_pmu:6325) CRITICAL: Failed assertion: perf_elapsed(&pm.metrics[0]) > (1-USAGE_TOLERANCE) * elapsed_ns(&start, &now)

Now. Looks like that by itself PMU context migration works. For example, if you will comment out
"perf_pmu_migrate_context(&pmu->base, cpu, target)" you will get:

Executed on rcs0 for 32004434918us
i915/rcs0-busy/: 76623707us

Compare with previous:
Executed on rcs0 for 32004262184us
i915/rcs0-busy/: 2225723999us

This test passed on the previous set of patches, I mean Tvrtko's v2 series + my patches.

So, it seems we are loosing counter values somehow. I saw in the patches that this place really was modified - you
have added subtraction from initial counter value:
static void i915_pmu_event_read(struct perf_event *event)
{

local64_set(&event->count,
__i915_pmu_event_read(event) -
local64_read(&event->hw.prev_count));
}

But looks like the problem is that with the PMU context migration we get sequence of events start/stop (or maybe
add/del) which eventually call our i915_pmu_enable/disable. Here is the dmesg log with the obvious printk:

[ 153.971096] [IGT] perf_pmu: starting subtest cpu_online
[ 153.971151] i915_pmu_enable: event->hw.prev_count=0
[ 154.036015] i915_pmu_disable: event->hw.prev_count=0
[ 154.048027] i915_pmu_enable: event->hw.prev_count=0
[ 154.049343] smpboot: CPU 0 is now offline
[ 155.059028] smpboot: Booting Node 0 Processor 0 APIC 0x0
[ 155.155078] smpboot: CPU 1 is now offline
[ 156.161026] x86: Booting SMP configuration:
[ 156.161027] smpboot: Booting Node 0 Processor 1 APIC 0x2
[ 156.197065] IRQ 122: no longer affine to CPU2
[ 156.198087] smpboot: CPU 2 is now offline
[ 157.208028] smpboot: Booting Node 0 Processor 2 APIC 0x4
[ 157.263093] smpboot: CPU 3 is now offline
[ 158.273026] smpboot: Booting Node 0 Processor 3 APIC 0x6
[ 158.310026] i915_pmu_disable: event->hw.prev_count=76648307
[ 158.319020] i915_pmu_enable: event->hw.prev_count=76648307
[ 158.319098] IRQ 124: no longer affine to CPU4
[ 158.320368] smpboot: CPU 4 is now offline
[ 159.326030] smpboot: Booting Node 0 Processor 4 APIC 0x1
[ 159.365306] smpboot: CPU 5 is now offline
[ 160.371030] smpboot: Booting Node 0 Processor 5 APIC 0x3
[ 160.421077] IRQ 125: no longer affine to CPU6
[ 160.422093] smpboot: CPU 6 is now offline
[ 161.429030] smpboot: Booting Node 0 Processor 6 APIC 0x5
[ 161.467091] smpboot: CPU 7 is now offline
[ 162.473027] smpboot: Booting Node 0 Processor 7 APIC 0x7
[ 162.527019] i915_pmu_disable: event->hw.prev_count=4347548222
[ 162.546017] i915_pmu_enable: event->hw.prev_count=4347548222
[ 162.547317] smpboot: CPU 0 is now offline
[ 163.553028] smpboot: Booting Node 0 Processor 0 APIC 0x0
[ 163.621089] smpboot: CPU 1 is now offline
[ 164.627028] x86: Booting SMP configuration:
[ 164.627029] smpboot: Booting Node 0 Processor 1 APIC 0x2
[ 164.669308] smpboot: CPU 2 is now offline
[ 165.679025] smpboot: Booting Node 0 Processor 2 APIC 0x4
[ 165.717089] smpboot: CPU 3 is now offline
[ 166.723025] smpboot: Booting Node 0 Processor 3 APIC 0x6
[ 166.775016] i915_pmu_disable: event->hw.prev_count=8574197312
[ 166.787016] i915_pmu_enable: event->hw.prev_count=8574197312
[ 166.788309] smpboot: CPU 4 is now offline
[ 167.794025] smpboot: Booting Node 0 Processor 4 APIC 0x1
[ 167.837114] smpboot: CPU 5 is now offline
[ 168.847025] smpboot: Booting Node 0 Processor 5 APIC 0x3
[ 168.889312] smpboot: CPU 6 is now offline
[ 169.899030] smpboot: Booting Node 0 Processor 6 APIC 0x5
[ 169.944104] smpboot: CPU 7 is now offline
[ 170.954032] smpboot: Booting Node 0 Processor 7 APIC 0x7
[ 171.000016] i915_pmu_disable: event->hw.prev_count=12815138319
[ 171.008017] i915_pmu_enable: event->hw.prev_count=12815138319
[ 171.009304] smpboot: CPU 0 is now offline
[ 172.017028] smpboot: Booting Node 0 Processor 0 APIC 0x0
[ 172.096104] smpboot: CPU 1 is now offline
[ 173.106025] x86: Booting SMP configuration:
[ 173.106026] smpboot: Booting Node 0 Processor 1 APIC 0x2
[ 173.147078] smpboot: CPU 2 is now offline
[ 174.153025] smpboot: Booting Node 0 Processor 2 APIC 0x4
[ 174.192093] smpboot: CPU 3 is now offline
[ 175.198028] smpboot: Booting Node 0 Processor 3 APIC 0x6
[ 175.229042] i915_pmu_disable: event->hw.prev_count=17035889079
[ 175.242030] i915_pmu_enable: event->hw.prev_count=17035889079
[ 175.242163] IRQ fixup: irq 120 move in progress, old vector 131
[ 175.242165] IRQ fixup: irq 121 move in progress, old vector 147
[ 175.242171] IRQ 124: no longer affine to CPU4
[ 175.243435] smpboot: CPU 4 is now offline
[ 176.248040] smpboot: Booting Node 0 Processor 4 APIC 0x1
[ 176.285328] smpboot: CPU 5 is now offline
[ 177.296039] smpboot: Booting Node 0 Processor 5 APIC 0x3
[ 177.325067] IRQ 125: no longer affine to CPU6
[ 177.326087] smpboot: CPU 6 is now offline
[ 178.335036] smpboot: Booting Node 0 Processor 6 APIC 0x5
[ 178.377063] IRQ 122: no longer affine to CPU7
[ 178.378086] smpboot: CPU 7 is now offline
[ 179.388028] smpboot: Booting Node 0 Processor 7 APIC 0x7
[ 179.454030] i915_pmu_disable: event->hw.prev_count=21269856967
[ 179.470026] i915_pmu_enable: event->hw.prev_count=21269856967
[ 179.471110] smpboot: CPU 0 is now offline
[ 180.481028] smpboot: Booting Node 0 Processor 0 APIC 0x0
[ 180.551075] smpboot: CPU 1 is now offline
[ 181.558029] x86: Booting SMP configuration:
[ 181.558030] smpboot: Booting Node 0 Processor 1 APIC 0x2
[ 181.595096] smpboot: CPU 2 is now offline
[ 182.605029] smpboot: Booting Node 0 Processor 2 APIC 0x4
[ 182.657084] smpboot: CPU 3 is now offline
[ 183.668030] smpboot: Booting Node 0 Processor 3 APIC 0x6
[ 183.709017] i915_pmu_disable: event->hw.prev_count=25497358644
[ 183.727016] i915_pmu_enable: event->hw.prev_count=25497358644
[ 183.728305] smpboot: CPU 4 is now offline
[ 184.734027] smpboot: Booting Node 0 Processor 4 APIC 0x1
[ 184.767090] smpboot: CPU 5 is now offline
[ 185.777036] smpboot: Booting Node 0 Processor 5 APIC 0x3
[ 185.823096] smpboot: CPU 6 is now offline
[ 186.829051] smpboot: Booting Node 0 Processor 6 APIC 0x5
[ 186.856350] smpboot: CPU 7 is now offline
[ 187.862051] smpboot: Booting Node 0 Processor 7 APIC 0x7
[ 187.871216] [IGT] perf_pmu: exiting, ret=99
[ 187.889199] Console: switching to colour frame buffer device 240x67
[ 187.889583] i915_pmu_disable: event->hw.prev_count=29754080941

And the result which I got in userspace for this run were
Executed on rcs0 for 32003587981us
i915/rcs0-busy/: 2247436461us

After that I decided to roll back the change with counting values which I mentioned before, i.e.:
static void i915_pmu_event_read(struct perf_event *event)
{

local64_set(&event->count,
__i915_pmu_event_read(event) /*-
local64_read(&event->hw.prev_count)*/);
}

And I got test PASSED :):
Executed on rcs0 for 32002282603us
i915/rcs0-busy/: 31998855052us
Subtest cpu_online: SUCCESS (33.950s)

At this point I need to go home :). Maybe you will have time to look into this issue? If not, I will continue
tomorrow.

Regards,
Dmitry.