From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Fushen Chen <fchen@apm.com>
Cc: Linuxppc-dev Development <linuxppc-dev@ozlabs.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: CONFIG_NO_HZ added too much idle time in /proc/stat during throughput test.
Date: Wed, 14 Dec 2011 10:24:10 +1100 [thread overview]
Message-ID: <1323818650.7671.3.camel@pasglop> (raw)
In-Reply-To: <CAEu=RPirE=H1N=KjHNjNRBM6H1fRvrugCw6ojqWaTNm2=WTfng@mail.gmail.com>
On Tue, 2011-12-13 at 12:42 -0800, Fushen Chen wrote:
> On APM82181, "vmstat" (/proc/stat) doesn't show correct idle
> percent, if kernel enables "CONFIG_NO_HZ" (Tickless System / Dynamic
> Tick).
>
> When I run wireless throughput test with heavy traffic, "vmstat" shows
> very high idle percent while "oprofile" shows very low idle percent.
> During the test, the system is idle, but network traffic uses a lot of
> hard IRQ and soft-irq time. "vmstat" would have the correct stats if
> account_idle_ticks(ticks) in kernel/time/tick-sched.c doesn't add more
> idle time in "vmstat". In the same test, if I disable "CONFIG_NO_HZ"
> in kernel, idle percent in "vmstat" and "oprofile" would match.
>
> My APM82181 kernel configuration is "CONFIG_NO_HZ", "CONFIG_HZ_250=y",
> "CONFIG_HZ=250", and "CONFIG_HIGH_RES_TIMERS".
>
> My question is that if kernel enables "CONFIG_NO_HZ", how would kernel
> report correct stats.
Hi Thomas ! Any idea what we're doing wrong ? :-)
Cheers,
Ben.
> Thanks,
> Fushen
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev
next prev parent reply other threads:[~2011-12-13 23:24 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-13 20:42 CONFIG_NO_HZ added too much idle time in /proc/stat during throughput test Fushen Chen
2011-12-13 23:24 ` Benjamin Herrenschmidt [this message]
2011-12-13 23:28 ` Thomas Gleixner
2011-12-13 23:34 ` Benjamin Herrenschmidt
2011-12-14 1:14 ` Fushen Chen
2011-12-14 3:17 ` Anton Blanchard
[not found] <CAEu=RPirE=H1N=KjHNjNRBM6H1fRvrugCw6ojqWaTNm2=WTfng__4707.66240400753$1323813396$gmane$org@mail.gmail.com>
2011-12-13 23:57 ` Andreas Schwab
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