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Re: Move to git is imminent - awaiting Stefan's approval

From: Bob Proulx
Subject: Re: Move to git is imminent - awaiting Stefan's approval
Date: Sun, 12 Jan 2014 14:29:31 -0700
User-agent: Mutt/1.5.21 (2010-09-15)

Achim Gratz wrote:
> Bob Proulx writes:
> >(Wondering if we can periodically run 'git gc --agressive' on the
> >larger git repositories at a niced background task priority but not too
> >often and still achieve a good benefit for the time between agressive
> >repacks.)
> Just a manual "git gc --aggressive" once in a while should be enough.
> If you are going to do it as a cron-job, I'm not sure if it's a good
> idea to nice it.

Due to the performance issues some of the Savannah admins have started
nicing background tasks as to hint to the scheduler.  Hoping that
interactive tasks get more priority.  Because at some times of day
there has been a problem with the server being slow enough to cause
timeouts.  Especially the web frontend to vcs.  Therefore if it isn't
a time critical task then running it niced is a hint to the scheduler.

The problem is that as a VM all of the system performance information
is fake data and can't show the actual system state.  And since we are
currently I/O limited at times the system is often blocked waiting for
I/O in which case the cpu priority doesn't matter.  There is more cpu
resource to go around than backplane disk I/O.  But from the VM itself
there isn't any useful performance data.  Only the FSF admins have
access to the dom0 and we count on them for real performance
information from it.  Unfortunately the FSF admin time to work on
server performance problems has been limited.

> I think you'd rather want to limit the number of threads it uses,
> which also limits the memory footprint, which is probably the bigger
> problem anyway and should probably be tuned further depending on how
> beefy the server is.

The dom0 server is an 8-core AMD Opteron running Xen for virtualization.
It has sufficient RAM.  But IMNHO too much I/O from all of the VMs
running on it.  The vcs VM is allocated seven xen cores.

The hint about threads is a good one and I will keep an eye on it.


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