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From "Krotil, Radek" <radek.kro...@siemens.com>
Subject Re: Better choice for Linux semaphore than spinlock?
Date Tue, 04 Feb 2020 11:01:40 GMT
Hi All.
I believe this issue originates at one of our customer and is related how Polarion ALM is
using Subversion at scale. This is a reoccurring issue being encountered by several enterprise
customers and I'd be more than happy to help the community to pin it down and get it fixed.
Has there been any update since October on this problem?
On the customer end the problem is easy to detect, where almost all CPU is consumed by svnserve
process, while more than 95% of the CPU is spent in system time, leaving almost no throughput
for the actual operation.
[cid:image001.png@01D5DB52.DAB45430]
Best regards,
Radek Krotil

Siemens Digital Industries Software
Polarion ALM Product Management
polarion.plm.automation.siemens.com<https://polarion.plm.automation.siemens.com/>


On 2019/10/12 23:29:44, eponymous alias <e...@yahoo.com> wrote:
>  Perhaps these links might be of help in some way:>
>
> https://webkit.org/blog/6161/locking-in-webkit/>
> https://blog.mozilla.org/nfroyd/2017/03/29/on-mutex-performance-part-1/>
> https://preshing.com/20111118/locks-arent-slow-lock-contention-is/>
>
> On Monday, October 7, 2019, 1:56:14 PM PDT, Doug Robinson <do...@wandisco.com>
wrote:>
>
> Rüdiger:>
>
> On Mon, Oct 7, 2019 at 3:51 PM Ruediger Pluem <rp...@apache.org> wrote:>
>
>  On 10/07/2019 08:40 PM, Branko Čibej wrote:>
>  > On Mon, 7 Oct 2019, 19:47 Doug Robinson, <doug.robinson@wandisco.com <ma...@wandisco.com>>
wrote:>
>  >>
>  > Folks:>
>  >>
>  > I spoke with this user late last week. They stated that they can only get approximately
400 parallel SVN operations>

>  > before the "system time" consumes all available CPU for an 8-core machine. Adding
more cores won't help because of>

>  > the nature of spin locks (it makes things worse). Turns out that even with ~100
parallel SVN operations the "system>

>  > time" starts becoming significant/measurable (~10%). Both HTTP (mod_dav_svn) and
"svnserve" protocols participate>

>  > in the lock contention.>
>  >>
>  > Your help would be greatly appreciated.>
>  >>
>  > Whew. So. Reducing this issue to "use a more efficient lock" is not going to work,
and you provided far too little>

>  > information to even attempt a diagnosis. For starters, I recommend gathering as
much info as possible (anonymised of>

>  > course) about the server configuration, everything from httpd an svnserve to the
repository config and underlying>

>  > filesystem, if possible. Getting stack traces of the "stuck" threads would be necessary,
too. Without knowing exactly>

>  > what is happening, these kinds of problems are extremely hard to understand, let
alone fix.>
>
>  Plus depending on which part of the code requires this lock a different locking mechanism
that might suit better for>

>  this use case can possibly be chosen via configuration changes (e.g. httpd allows this
for most of its locking).>
>
> That would be awesome! I'll definitely try to get those stack tracebacks.>
>
> Cheers.>
>
> Doug>
>   >

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