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Message-ID: <50F062B3.6070104@redhat.com> Date: Fri, 11 Jan 2013 13:06:27 -0600 From: Eric Sandeen <sandeen@...hat.com> To: Jan Kara <jack@...e.cz> CC: "Theodore Ts'o" <tytso@....edu>, ext4 development <linux-ext4@...r.kernel.org> Subject: Re: [PATCH RFC] jbd: don't wake kjournald unnecessarily On 1/11/13 1:03 PM, Jan Kara wrote: > On Fri 11-01-13 10:42:00, Eric Sandeen wrote: ... >> TBH though, this is somewhat opposite of what I'd expect; I thought more >> wakes might mean smaller transactions - except the wakes were "pointless" >> - so I'm not quite sure what's going on yet. We can certainly see the >> difference, though, and that my change gets us back to the prior >> behavior. > Yes, that's what I'd expect if the difference was really in IO. But > apparently the benchmark is CPU bound on the machine and so the higher > amount of work we do under j_state_lock (wake_up() has some small > cost after all - it disables interrupts and takes q->lock) results in > kjournald taking longer to wake and do its work. It might be interesting to > know about how many useless wakeups are we speaking here? Yeah, I want to get that next. I think I'll need to instrument the module to get that, the fear is that systemtap might have too much overhead (but I can try both ways). Thanks, -Eric > Honza > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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