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Re: Better choice for Linux semaphore than spinlock?

From: Doug Robinson <doug.robinson_at_wandisco.com>
Date: Mon, 7 Oct 2019 16:55:52 -0400


On Mon, Oct 7, 2019 at 3:51 PM Ruediger Pluem <rpluem_at_apache.org> wrote:

> On 10/07/2019 08:40 PM, Branko Čibej wrote:
> > On Mon, 7 Oct 2019, 19:47 Doug Robinson, <doug.robinson_at_wandisco.com
> <mailto:doug.robinson_at_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.



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Received on 2019-10-07 22:56:10 CEST

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