Re: Proposal: Use hi-res clock for file timestamps

[Andi Kleen]

"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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