linux-kernel - Re: [patch 1/2]percpu

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Message-ID: <20140210154917.GC320@dhcp-26-207.brq.redhat.com>
Date:	Mon, 10 Feb 2014 16:49:17 +0100
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Kent Overstreet <kmo@...erainc.com>, Jens Axboe <axboe@...nel.dk>,
	Shaohua Li <shli@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2]percpu_ida: fix a live lock

On Mon, Feb 10, 2014 at 01:29:42PM +0100, Alexander Gordeev wrote:
> > We'll defintively need a fix to be able to allow the whole tag space.
> > For large numbers of tags per device the flush might work, but for
> > devices with low number of tags we need something more efficient.  The
> > case of less tags than CPUs isn't that unusual either and we probably
> > want to switch to an allocator without per cpu allocations for them to
> > avoid all this.  E.g. for many ATA devices we just have a single tag,
> > and many scsi drivers also only want single digit outstanding commands
> > per LUN.
> 
> Do we really always need the pool for these classes of devices?
> 
> Pulling tags from local caches to the pool just to (near to) dry it at
> the very next iteration does not seem beneficial. Not to mention caches
> vs pool locking complexities.

And I meant here we do not scrap per cpu allocations.

-- 
Regards,
Alexander Gordeev
agordeev@...hat.com
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