From: Kent Overstreet <kmo@daterainc.com>
To: Rolf Fokkens <rolf@rolffokkens.nl>
Cc: linux-bcache@vger.kernel.org
Subject: Re: bcache_writebac task 100% CPU
Date: Mon, 19 May 2014 09:55:50 -0700 [thread overview]
Message-ID: <20140519165550.GD2276@kmo> (raw)
In-Reply-To: <53786E02.8060300@rolffokkens.nl>
On Sun, May 18, 2014 at 10:23:30AM +0200, Rolf Fokkens wrote:
> Sometimes bcache_writebac task consumes 100% CPU during normal operation, but after a while (like a minute) this drops to normal.
>
> It can be triggered in a reproducable fashion on my system by:
>
> echo 0 > /sys/block/bcache0/bcache/writeback_percent
>
> After this bcache_writebac starts to burn CPU cycles, and it never seems to stop doing so. changing the writeback_percent value back to 25 doesn't change anything.
>
> Apart from a busy CPU there appear to be no problem (e.g. no "task bcache_writebac:286 blocked for more than 120 seconds" messages).
...Changing it back to 25% doesn't do anything? _that_ is odd...
Can you send me the output of writeback_rate_debug? Check it once before you've
done anything, when things are working normally (after a fresh boot when
writeback_percent is nonzero, probably), then grab it again after you've set
writeback_percent to 0 and then back to 25, when it's still spinning.
There seems to be two separate bugs here, the one I'm particularly concerned
about is why setting writeback_percent back to 25 doesn't restore the old
behaviour.
Also, what kernel are you running?
next prev parent reply other threads:[~2014-05-19 16:55 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-18 8:23 bcache_writebac task 100% CPU Rolf Fokkens
2014-05-19 16:55 ` Kent Overstreet [this message]
2014-05-19 18:01 ` Rolf Fokkens
2014-05-20 19:38 ` Rolf Fokkens
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