Messages in this thread | | | Subject | Re: [PATCH 1/3] clocksource/mips-gic-timer: Fix rcu_sched timeouts from multithreading | From | Daniel Lezcano <> | Date | Thu, 19 Oct 2017 11:09:02 +0200 |
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On 11/10/2017 16:01, Matt Redfearn wrote: > When the MIPS GIC clockevent code was written, it appears to have > inherited the 0x300 cycle min delta from the MIPS CPU timer driver. This > is suboptimal for two reasons. > > Firstly, the CPU timer counts once every other cycle (i.e. half the > clock rate). The GIC counts once per clock. Assuming that the GIC and > CPU share the same clock this means the GIC is counting twice as fast, > and so the min delta should be (at least) doubled. Fix this by doubling > the min delta to 0x600. > > Secondly, the fixed min delta ignores the fact that with MIPS > multithreading active, execution resource within a core is shared > between the hardware threads within that core. An inconvenienly timed > switch of executing thread within gic_next_event, between the read and > write of updated count, can result in the CPU writing an event in the > past, and subsequently not receiving a tick interrupt until the counter > wraps. This stalls the CPU from the RCU scheduler. Other CPUs detect > this and print rcu_sched timeout messages in the kernel log. It can > lead to other issues as well if the CPU is holding locks or other > resources at the point at which it stalls. Fix this by scaling the min > delta for the timer based on the number of threads in the core > (smp_num_siblings). This accounts for the greater average runtime of > CPUs within a multithreading core. > > Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com> > Fixes: b695d8e6ad6f ("clocksource: mips-gic: Use clockevents_config_and_register") > Cc: <stable@vger.kernel.org> # v3.19 + > > Signed-off-by: Matt Redfearn <matt.redfearn@mips.com> > ---
Matt,
I'm dropping your series.
The first patch fails to compile because of the smp_num_siblings variable undefined when compile testing on another arch (probably a header is missing).
The issue the patch address could be fixed in the time framework as stated by Thomas.
As spotted by Thomas also, the local_irq_save() is not needed in the set_next_event() function, so the second patch is pointless and a patch removing those local_irq_save()/restore() would make more sense.
The third patch does not longer apply after removing the two above.
-- Daniel
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