linux-kernel - Re: [PATCH v3 next/akpm] aio: convert the ioctx list to radix tree

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Date:	Fri, 14 Jun 2013 17:20:40 +0300
From:	Octavian Purdila <octavian.purdila@...el.com>
To:	Zach Brown <zab@...hat.com>
Cc:	Benjamin LaHaise <bcrl@...ck.org>,
	Kent Overstreet <koverstreet@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-aio@...ck.org,
	linux-s390@...r.kernel.org, schwidefsky@...ibm.com,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v3 next/akpm] aio: convert the ioctx list to radix tree

On Wed, Jun 12, 2013 at 10:40 PM, Zach Brown <zab@...hat.com> wrote:
>> I've got an alternate approach for fixing this wart in lookup_ioctx()...
>> Instead of using an rbtree, just use the reserved id in the ring buffer
>> header to index an array pointing the ioctx.  It's not finished yet, and
>> it needs to be tidied up, but is most of the way there.
>
> Yeah, that might work.
>
> Note that the patch wasn't using an rbtree, it was storing the pointer
> value in a *radix* which is why single lookups took so long.  Presumably
> radix was used for RCU lookups.
>
> Your ring->id trick lets us use RCU with small ints instead of the
> context pointer.  It might be worth using idr instead of rolling manual
> array code.  It'd still be much faster than the list, but get rid of the
> large alloc, array walking, memcpy(), etc.
>

I picked up Ben's patch and incorporated Zach's idea and the first
results look promising, as expected. I am going to do a full test with
the same workload I've used for rbtree and come back with the results
and the patch in a day or so.

Thanks everybody !
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