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Re: [dm-devel] [PATCH v10 4/8] block: Add bio_reset()

On 2012-09-07 15:55, Jens Axboe wrote:
> On 2012-09-07 14:58, Kent Overstreet wrote:
>> On Thu, Sep 06, 2012 at 07:34:18PM -0600, Jens Axboe wrote:
>>> On 2012-09-06 16:34, Kent Overstreet wrote:
>>>> Reusing bios is something that's been highly frowned upon in the past,
>>>> but driver code keeps doing it anyways. If it's going to happen anyways,
>>>> we should provide a generic method.
>>>> This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c
>>>> was open coding it, by doing a bio_init() and resetting bi_destructor.
>>>> This required reordering struct bio, but the block layer is not yet
>>>> nearly fast enough for any cacheline effects to matter here.
>>> That's an odd and misplaced comment. Was just doing testing today at 5M
>>> IOPS, and even years back we've had cache effects for O_DIRECT in higher
>>> speed setups.
>> Ah, I wasn't aware that you were pushing that many iops through the
>> block layer - most I've tested myself was around 1M. It wouldn't
>> surprise me if cache effects in struct bio mattered around 5M...
> 5M is nothing, just did 13.5M :-)
> But we can reshuffle for now. As mentioned, we're way overdue for a
> decent look at cache profiling in any case.

No ill effects seen so far, fwiw:

  read : io=1735.8GB, bw=53690MB/s, iops=13745K, runt= 33104msec

Jens Axboe

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