Messages in this thread | | | Date | Sun, 31 Aug 2008 18:55:54 +0200 | From | Willy Tarreau <> | Subject | Re: [patch v2 0/5] Nano/Microsecond resolution for select() and poll() |
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Hi Arjan,
On Sun, Aug 31, 2008 at 09:28:28AM -0700, Arjan van de Ven wrote: > One thing to note is that on my machine, the current select() implementation > will return after 1997 microseconds when asked for 1999 microseconds; this > can be seen in a zoom in of the graph above: > http://www.tglx.de/~arjan/zoom.png > E.g. select() is returning too early in current Linux kernels; and this is > also fixed (by nature) by this patch series.
This is a good news. I've been bothered by this problem for a long time and got used to add 99999 us to any delay fed to select() (that started when HZ=100). I remember having noticed performance improvements in my applications using this trick even on other systems, so I don't think that Linux is the only one with this anomaly. I think it's simply caused by the rounding methods which make it hard to compute an accurate deadline when a value is converted before being added to jiffies.
I do not remember noticing this on epoll though. Maybe it's just because I did not look close enough :-/
Cheers, Willy
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