From: Alexander Gordeev <agordeev@redhat.com>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Jens Axboe <axboe@kernel.dk>, Kent Overstreet <kmo@daterainc.com>,
Shaohua Li <shli@kernel.org>, Christoph Hellwig <hch@lst.de>,
Mike Christie <michaelc@cs.wisc.edu>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] percpu_ida: Handle out-of-tags gracefully
Date: Tue, 11 Mar 2014 21:48:28 +0100 [thread overview]
Message-ID: <20140311204826.GA30105@dhcp-26-207.brq.redhat.com> (raw)
In-Reply-To: <531F518A.1070808@acm.org>
On Tue, Mar 11, 2014 at 07:10:18PM +0100, Bart Van Assche wrote:
> > I assume the BUG() above hits? If so, I am failing to understand how
> > the code gets here. Mind elaborate?
>
> Hello Alexander,
>
> You are correct, the BUG() mentioned in the call stack in the
> description of this patch does indeed correspond with the BUG()
> statement in the above code. That BUG() was encountered while testing
> the scsi-mq patch series with a workload with a large queue depth. I
> think the fact that I hit that BUG() statement means that my workload
> was queueing requests faster than these were processed by the SCSI LLD
> and hence that percpu_ida_alloc() ran out of tags.
Function steal_tags() is entered with disabled interrupts and
pool->lock taken. Then the 'for' cycle enters/loops while 'cpus_have_tags'
is not zero. Which means we can not end up with no set bits at all -
and that is the reason why BUG() is (legitimately) placed there.
> Bart.
--
Regards,
Alexander Gordeev
agordeev@redhat.com
next prev parent reply other threads:[~2014-03-11 20:47 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-10 14:12 Bart Van Assche
2014-03-11 13:51 ` Alexander Gordeev
2014-03-11 18:10 ` Bart Van Assche
2014-03-11 20:48 ` Alexander Gordeev [this message]
2014-03-12 7:22 ` Bart Van Assche
2014-03-12 8:41 ` Alexander Gordeev
2014-03-12 10:05 ` Bart Van Assche
2014-03-12 15:21 ` Alexander Gordeev
2014-03-12 16:16 ` Bart Van Assche
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