lkml.org 
[lkml]   [2011]   [Nov]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [GIT PULL] Queue free fix (was Re: [PATCH] block: Free queue resources at blk_release_queue())
On 2011-09-28 21:05, Eric Seppanen wrote:
> On Wed, Sep 28, 2011 at 11:16 AM, Christoph Hellwig <hch@infradead.org> wrote:
>> Right now on high iops device queue_lock is the major killer for
>> performance. It's one major reason (*) why a lot of the high iops devices
>> are all moving to ->make_request, which has other issues.
>>
>> (*) others are struct request allocation and the pointless merge hash
>
> I agree: queue lock is the worst performance killer when hw can do
>> 100K IOPS per block device.
>
> Rather than just being chased away from the request queue due to
> performance issues, I could argue there's very little point to having
> a queue for devices that
> (a) have no seek penalty (and always use noop elevator)
> (b) have hardware queues at least as deep as the default request queue
> (c) don't benefit from merging
>
> (c) is maybe debatable, but if a device can saturate its bus bandwidth
> on 4KB IO, the latency is probably not worth it.

I agree on a+b, but c is definitely more than debatable. I have yet to
see a device saturate its bandwidth on 4KB IOS. So merging on the write
side is always going to be a win.

--
Jens Axboe



\
 
 \ /
  Last update: 2011-11-30 11:21    [W:0.090 / U:0.396 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site