Re: [RFC, PATCH] Avoid hot statistics cache line in ext4 extent cache

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Fri, Apr 13, 2012 at 02:37:22PM -0400, Ted Ts'o wrote:
> On Fri, Apr 13, 2012 at 11:31:16AM -0700, Tim Chen wrote:
> > 
> > Benchmark is working on files on normal hard disk.  
> > However, I have I have a large number
> > of processes (80 processes, one for each cpu), each reading
> > a separate mmaped file.  The files are in the same directory.
> > That makes cache line bouncing on the counters particularly bad
> > due to the large number of processes running.
> 
> OK, so this is with an 80 CPU machine?

4 sockets, 40 cores, 80 threads.

> 
> And when you say 20% speed up, do you mean to say we are actually
> being CPU constrained when reading from files on a normal hard disk?

The files are in memory, but we're still CPU constrained due to various
other issues.

> The reason why I ask this is we're seeing anything like this with Eric
> Whitney's 48 CPU scalability testing; we're not CPU bottlenecked, and
> I don't even see evidence of a larger than usual CPU utilization
> compared to other file systems.

I bet Eric didn't test with this statistic counter.

> Ultimately, this isn't a regression and if Linus is willing to take a

The old kernel didn't have that problem, so it's a regression.

> change at this point, I'm willing to send it --- but I really don't
> understand the urgency.

If we don't fix performance regressions before each release then Linux
will get slower and slower. At least I don't want a slow Linux.

-Andi
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [Reiser Filesystem Development]     [Ceph FS]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux FS]     [Yosemite National Park]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Device Mapper]     [Linux Media]

  Powered by Linux