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SubjectRe: [4.2, Regression] Queued spinlocks cause major XFS performance regression
On 09/04/2015 01:48 AM, Dave Chinner wrote:
> Hi Waiman,
>
> For the first time in months I just turned of spinlock debugging on
> my performance test machine and I just got an unpleasant surprise on
> my standard inode allocation and reclaim test. I've described this
> test to you before, because it's found regressions in your previous
> lock scaling changes:
>
> http://permalink.gmane.org/gmane.linux.kernel/1768786
>
> This time it is the fsmark run that I use to populate the filesystem
> that is demonstrating a locking regression. I'll asked you before
> if you could add this test to your lock scaling regression test
> suite; please do it this time.
>
> Now, the regression. With spinlock debugging turned on, the
> performance of my usual XFS inode allocation benchmark using fsmark
> reports performance like this:
>
> FSUse% Count Size Files/sec App Overhead
> 0 1600000 0 312594.0 9944159
> 0 3200000 0 295668.6 10399679
> 0 4800000 0 279026.1 11397617
> .....
>
> This has been pretty stable for several releases - it varies +/- a
> few percent, but it's pretty much been like this since about 3.2
> when CONFIG_XFS_DEBUG=n, with or without basic spinlock debugging.
>
> When I turned spinlock debugging off on 4.2 to get some perf numbers
> a request from Linus, I got this:
>
> FSUse% Count Size Files/sec App Overhead
> 0 1600000 0 114143.9 9597599
> 0 3200000 0 95486.9 9460413
> 0 4800000 0 93918.2 9784699
> .

I am sorry that I was on vacation over the past weekend and so was not
able to respond in a timely manner. As Peter already has a patch to
address the root cause of this problem. I think this problem is all set.

Cheers,
Longman



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