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Message-ID: <1465904254.3529.234.camel@decadent.org.uk>
Date: Tue, 14 Jun 2016 12:37:34 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
akpm@...ux-foundation.org, Chris Wilson <chris@...is-wilson.co.uk>,
Jani Nikula <jani.nikula@...el.com>,
Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
Antti Koskipää
<antti.koskipaa@...ux.intel.com>
Subject: Re: [PATCH 3.16 012/114] drm/i915: Exit cherryview_irq_handler()
after one pass
On Tue, 2016-06-14 at 13:47 +0300, Ville Syrjälä wrote:
> 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.
But this has not been re-reverted in mainline, has it? Is it that
3.16-stable would need more changes backported to make this work, or is
mainline currently broken on Cherryview hardware?
Ben.
> >
> > ------------------
> >
> > From: Chris Wilson <chris@...is-wilson.co.uk>
> >
> > commit 9dbaab56ac09f07a73fe83bf69bec3e31060080a upstream.
> >
> > This effectively reverts
> >
> > commit 8e5fd599eb219f1054e39b40d18b217af669eea9
> > Author: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > 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] [] dump_stack+0x4f/0x72
> > [ 575.217994] [] watchdog_overflow_callback+0x151/0x160
> > [ 575.218003] [] __perf_event_overflow+0xa0/0x1e0
> > [ 575.218016] [] perf_event_overflow+0x14/0x20
> > [ 575.218028] [] intel_pmu_handle_irq+0x1da/0x460
> > [ 575.218042] [] ? poll_idle+0x3e/0x70
> > [ 575.218052] [] ? poll_idle+0x3e/0x70
> > [ 575.218064] [] perf_event_nmi_handler+0x28/0x50
> > [ 575.218075] [] nmi_handle+0x60/0x130
> > [ 575.218086] [] ? poll_idle+0x3e/0x70
> > [ 575.218096] [] do_nmi+0x140/0x470
> > [ 575.218108] [] end_repeat_nmi+0x1a/0x1e
> > [ 575.218119] [] ? poll_idle+0x3e/0x70
> > [ 575.218129] [] ? poll_idle+0x3e/0x70
> > [ 575.218139] [] ? poll_idle+0x3e/0x70
> > [ 575.218148] <> [] cpuidle_enter_state+0xf3/0x2f0
> > [ 575.218164] [] cpuidle_enter+0x17/0x20
> > [ 575.218175] [] call_cpuidle+0x2a/0x40
> > [ 575.218185] [] cpu_startup_entry+0x273/0x330
> > [ 575.218196] [] 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@...is-wilson.co.uk>
> > Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > Cc: Antti Koskipää <antti.koskipaa@...ux.intel.com>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@...el.com>
> > Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@...el.com>
> > Reviewed-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > Link: http://patchwork.freedesktop.org/patch/msgid/1457946117-6714-1-git-send-email-chris@chris-wilson.co.uk
> > (cherry picked from commit 579de73b048a0a4c66c25a033ac76a2836e0cf73)
> > Signed-off-by: Jani Nikula <jani.nikula@...el.com>
> > Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> > ---
> > 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;
> > }
>
--
Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
- Albert
Camus
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