Re: [Bugme-new] [Bug 16321] New: os unresponsive during buffered I/O

[Andrew Morton <akpm@linux-foundation.org>]

On Sat, 03 Jul 2010 13:56:13 +0200 Jens Axboe <axboe@kernel.dk> wrote:

> On 03/07/10 01.05, Andrew Morton wrote:
> > On Thu, 1 Jul 2010 11:57:37 GMT
> > bugzilla-daemon@bugzilla.kernel.org wrote:
> > 
> >> https://bugzilla.kernel.org/show_bug.cgi?id=16321
> >>
> >>            Summary: os unresponsive during buffered I/O
> >>            Product: IO/Storage
> >>            Version: 2.5
> >>     Kernel Version: 2.6.34
> >>           Platform: All
> >>         OS/Version: Linux
> >>               Tree: Mainline
> >>             Status: NEW
> >>           Severity: normal
> >>           Priority: P1
> >>          Component: Block Layer
> >>         AssignedTo: axboe@kernel.dk
> >>         ReportedBy: rrs@researchut.com
> >>         Regression: No
> >>
> >>
> >> I have been running these tests on my laptop running the 2.6.34 Debian kernel.
> >> When doing buffered I/O, the OS completely stalls to any interactivity. I
> >> cannot switch console tabs in my Desktop Environment and the mouse pointer does
> >> not move.
> >>
> >> Eventually, I/O completes and every thing resumes to normal. There is no OOM
> >> seen during the I/O operation.
> >> If doing direct I/O, interactivity does not get penalized.
> >>
> > 
> > 1...
> > 
> > 2...
> > 
> > 3...
> > 
> > FUCK!!!
> > 
> > We've been trying to fix this stuff for ten years.  Apparently, without
> > success.  Do we suck, or what?
> 
> We suck. This is assigned to the block layer, but it must be something
> a lot more fundemental than this. Either the vm is shitting itself, or
> something else is sucking up the juice completely. Or the CPU scheduler
> is going to pieces, I dunno. The report says that he cannot even move the
> mouse or switch console tabs, clearly we are not (only) dealing with
> an issue at the IO side.
> 
> What else is interesting is that only a few people seem to see this.
> What is different about their setup or their hardware?! I cannot
> reproduce reports like this, and if it happened for everybody for
> a simple 4 process random write like this, then everything would
> grind to a halt.
> 
> I propose we fly Andrew out to investigate in person :-)

Hey, I suck more than anyone!

My laptop goes absolutely utterly mouse-wont-move comatose for tens of
minutes when it fetchmails 100 emails and 100 spamassassins go berzerk.
It could be either a CPU scheduler thing, or an IO thing, or an evil
combination of both.

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