Re: Proposal: Use hi-res clock for file timestamps
From: Andi Kleen
Date: Tue Aug 17 2010 - 10:54:16 EST
"Patrick J. LoPresti" <lopresti@xxxxxxxxx> writes:
>
> 1) Anybody who cares about file system performance is already using
> "noatime" or "relatime", which mitigates the hit greatly.
Consider mtime.
> If the above patch is too slow for some architectures, how about
> making it a configuration option? Call it "CONFIG_1980S_FILE_TICK",
> have it default to YES on the architectures that care and NO on
> anything remotely modern and sane.
>
> OK that's my proposal. Bash away.
I suspect it will be a performance disaster on x86 for VFS intensive
applications on capable file systems. VFS is very performance
critical. These checks lurk on unexpected places too, e.g. on /dev
access.
Even TSC is much slower than just reading the variable.
Also you should check if the file system granuality
even supports it, it's completely wasted on a ext3 for example.
Maybe as a optional sysctl, default to off.
-Andi
--
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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