Re: [PATCH/RFC v3 7/9] write_entry(): use fstat() instead of lstat() when file is open

From: Johannes Sixt <j.sixt@viscovery.net>
Date: Feb 5, 2009, 08:14 UTC
Message-ID: <498A9FD3.2020601@viscovery.net>
In-Reply-To: <86tz7ayo51.fsf_-_@broadpark.no>

Kjetil Barvik schrieb:

>   And, yes, since each lstat() call cost approximately 44 microseconds
>   compared to 12-16 for each lstat() on my Linux box, there was a little

                               ^^^^^^^ fstat()?

>   performance gain from this patch.

This does look like a good gain. But do you have hard numbers that back the claim?

If you can squeeze out a 10% improvement on Linux with this patch, we should take it, and if it turns out that it doesn't work on Windows, we could trivially throw in an #ifdef MINGW (or even #ifdef WIN32 if Cygwin is affected, too) that skips the fstat() optimization.

But we really should have numbers that justify this effort.

BTW, the statement from the Windows documentation was:

  "The only guarantee about a file timestamp is that the file time is
   correctly reflected when the handle that makes the change is closed."

In the case of this patch, the timestamp is queried via the handle that made the change, and in this case special case the timestamp could be correct nevertheless. The guarantee doesn't cover this case, but it would be natural, and perhaps it Just Works?

-- Hannes