Re: [PATCH 3.16 012/114] drm/i915: Exit cherryview_irq_handler() after one pass
From: Ville Syrjälä
Date: Tue Jun 14 2016 - 06:47:20 EST
On Mon, Jun 13, 2016 at 07:36:37PM +0100, Ben Hutchings wrote:
> 3.16.36-rc1 review patch. If anyone has any objections, please let me know.
Do not backport this one. It'll break things.
>
> ------------------
>
> From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>
> commit 9dbaab56ac09f07a73fe83bf69bec3e31060080a upstream.
>
> This effectively reverts
>
> commit 8e5fd599eb219f1054e39b40d18b217af669eea9
> Author: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Date: Wed Apr 9 13:28:50 2014 +0300
>
> drm/i915/chv: Make CHV irq handler loop until all interrupts are consumed
>
> as under continuous execlists load we can saturate the IRQ handler,
> destablising the tsc clock and triggering the NMI watchdog to declare a hung
> CPU.
>
> [ 552.756051] clocksource: timekeeping watchdog on CPU0: Marking clocksource 'tsc' as unstable because the skew is too large:
> [ 552.756080] clocksource: 'refined-jiffies' wd_now: 10003b480 wd_last: 10003b28c mask: ffffffff
> [ 552.756091] clocksource: 'tsc' cs_now: d55d31aa50 cs_last: d17446166c mask: ffffffffffffffff
> [ 552.756210] clocksource: Switched to clocksource refined-jiffies
> [ 575.217870] NMI watchdog: Watchdog detected hard LOCKUP on cpu 1
> [ 575.217893] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.5.0-rc7+ #18
> [ 575.217905] Hardware name: /NUC5CPYB, BIOS PYBSWCEL.86A.0027.2015.0507.1758 05/07/2015
> [ 575.217915] 0000000000000000 ffff88027fd05bc0 ffffffff81288c6d 0000000000000000
> [ 575.217935] 0000000000000001 ffff88027fd05be0 ffffffff810e72d1 0000000000000000
> [ 575.217951] ffff88027fd05c80 ffff88027fd05c20 ffffffff81114b60 0000000181015f1e
> [ 575.217967] Call Trace:
> [ 575.217973] <NMI> [<ffffffff81288c6d>] dump_stack+0x4f/0x72
> [ 575.217994] [<ffffffff810e72d1>] watchdog_overflow_callback+0x151/0x160
> [ 575.218003] [<ffffffff81114b60>] __perf_event_overflow+0xa0/0x1e0
> [ 575.218016] [<ffffffff811154c4>] perf_event_overflow+0x14/0x20
> [ 575.218028] [<ffffffff8101d2ca>] intel_pmu_handle_irq+0x1da/0x460
> [ 575.218042] [<ffffffff814a8aae>] ? poll_idle+0x3e/0x70
> [ 575.218052] [<ffffffff814a8aae>] ? poll_idle+0x3e/0x70
> [ 575.218064] [<ffffffff81014ae8>] perf_event_nmi_handler+0x28/0x50
> [ 575.218075] [<ffffffff81007540>] nmi_handle+0x60/0x130
> [ 575.218086] [<ffffffff814a8aae>] ? poll_idle+0x3e/0x70
> [ 575.218096] [<ffffffff810079c0>] do_nmi+0x140/0x470
> [ 575.218108] [<ffffffff81559ec7>] end_repeat_nmi+0x1a/0x1e
> [ 575.218119] [<ffffffff814a8aae>] ? poll_idle+0x3e/0x70
> [ 575.218129] [<ffffffff814a8aae>] ? poll_idle+0x3e/0x70
> [ 575.218139] [<ffffffff814a8aae>] ? poll_idle+0x3e/0x70
> [ 575.218148] <<EOE>> [<ffffffff814a8353>] cpuidle_enter_state+0xf3/0x2f0
> [ 575.218164] [<ffffffff814a8587>] cpuidle_enter+0x17/0x20
> [ 575.218175] [<ffffffff810aaa3a>] call_cpuidle+0x2a/0x40
> [ 575.218185] [<ffffffff810aade3>] cpu_startup_entry+0x273/0x330
> [ 575.218196] [<ffffffff81033a1e>] start_secondary+0x10e/0x130
>
> However, not servicing all available IIR within the handler does hurt the
> throughput of pathological nop execbuf by about 20%, with a similar effect
> upon the dispatch latency of a series of execbuf.
>
> v2: use do {} while(0) for a smaller patch, and easier to revert again
>
> I have reasonable confidence that we do not miss GT interrupts (as
> execlists provides a stress case with a failure mechanism easily
> detected by igt), however I have less confidence about all the other
> sources of interrupts and worry that may lose a display hotplug
> interrupt, for example.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93467
> Testcase: igt/gem_exec_nop/basic # requires NMI watchdog
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Antti Koskipää <antti.koskipaa@xxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Link: http://patchwork.freedesktop.org/patch/msgid/1457946117-6714-1-git-send-email-chris@xxxxxxxxxxxxxxxxxx
> (cherry picked from commit 579de73b048a0a4c66c25a033ac76a2836e0cf73)
> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_irq.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1875,7 +1875,7 @@ static irqreturn_t cherryview_irq_handle
> u32 master_ctl, iir;
> irqreturn_t ret = IRQ_NONE;
>
> - for (;;) {
> + do {
> master_ctl = I915_READ(GEN8_MASTER_IRQ) & ~GEN8_MASTER_IRQ_CONTROL;
> iir = I915_READ(VLV_IIR);
>
> @@ -1897,7 +1897,7 @@ static irqreturn_t cherryview_irq_handle
> POSTING_READ(GEN8_MASTER_IRQ);
>
> ret = IRQ_HANDLED;
> - }
> + } while (0);
>
> return ret;
> }
--
Ville Syrjälä
Intel OTC