linux-kernel - Re: perf on 2.6.38-rc4 wedges my box

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Date:	Wed, 09 Feb 2011 10:47:10 -0700
From:	David Ahern <dsahern@...il.com>
To:	Jeff Moyer <jmoyer@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: perf on 2.6.38-rc4 wedges my box



On 02/09/11 10:38, Jeff Moyer wrote:
> Hi,
> 
> I'm trying out willy's ata_ram driver[1], and in so doing have managed to
> wedge my box while using perf record on an aio-stress run:
> 
> [root@...allica ~]# modprobe ata_ram capacity=2097152 preallocate=1
> [root@...allica ~]# ./aio-stress -O -o 0 -r 4 -d 32 -b 16 /dev/sds
> adding stage write
> starting with write
> file size 1024MB, record size 4KB, depth 32, ios per iteration 8
> max io_submit 16, buffer alignment set to 4KB
> threads 1 files 1 contexts 1 context offset 2MB verification off
> adding file /dev/sds thread 0
> write on /dev/sds (621.30 MB/s) 1024.00 MB in 1.65s
> thread 0 write totals (621.27 MB/s) 1024.00 MB in 1.65s
> [root@...allica ~]# perf record -- ./aio-stress -O -o 0 -r 4 -d 32 -b 16
> /dev/sds

Have you tried '-e cpu-clock' for S/W based profiling vs the default H/W
profiling? Add -v to see if the fallback to S/W is happening now.

David


> adding stage write
> starting with write
> file size 1024MB, record size 4KB, depth 32, ios per iteration 8
> max io_submit 16, buffer alignment set to 4KB
> threads 1 files 1 contexts 1 context offset 2MB verification off
> adding file /dev/sds thread 0
> 
> and there it sits.  On the console, I see:
> 
> NOHZ: local_softirq_pending 100
> NOHZ: local_softirq_pending 100
> NOHZ: local_softirq_pending 100
> NOHZ: local_softirq_pending 100
> NOHZ: local_softirq_pending 100
> 
> The number of messages varies, but this is the most I've seen (it
> doesn't keep repeating).  At this point, the machine does not respond to
> pings.  As I don't have physical access at the moment, I can't try
> alt-sysrq, but might be able to do that tomorrow.  It's probably worth
> noting that I've witnessed similar behavior with real devices, so it's
> not just the ata_ram driver.
> 
> Any ideas on how to track this down?
> 
> Thanks!
> 
> Jeff
> 
> [1] http://git.kernel.org/?p=linux/kernel/git/willy/misc.git;a=shortlog;h=refs/heads/ata-ram
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