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Message-ID: <20080112012626.GI28570@kvack.org> Date: Fri, 11 Jan 2008 20:26:26 -0500 From: Benjamin LaHaise <bcrl@...ck.org> To: dipankar@...ibm.com, Andrew Morton <akpm@...ux-foundation.org> Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org Subject: [PATCH/RFC] synchronize_rcu(): high latency on idle system Hello folks, I'd like to put the patch below out for comments to see if folks think the approach is a valid fix to reduce the latency of synchronize_rcu(). The motivation is that an otherwise idle system takes about 3 ticks per network interface in unregister_netdev() due to multiple calls to synchronize_rcu(), which adds up to quite a few seconds for tearing down thousands of interfaces. By flushing pending rcu callbacks in the idle loop, the system makes progress hundreds of times faster. If this is indeed a sane thing to, it probably needs to be done for other architectures than x86. And yes, the network stack shouldn't call synchronize_rcu() quite so much, but fixing that is a little more involved. -ben diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c index 9663c2a..592f6e4 100644 --- a/arch/x86/kernel/process_32.c +++ b/arch/x86/kernel/process_32.c @@ -188,6 +188,9 @@ void cpu_idle(void) rmb(); idle = pm_idle; + if (rcu_pending(cpu)) + rcu_check_callbacks(cpu, 0); + if (!idle) idle = default_idle; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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