Performance benefit of epoll over poll
keithp at keithp.com
Thu May 26 07:41:29 UTC 2016
epoll is designed to reduce the cost of having many file descriptors
in a process which are mostly idle. The kernel only reports data about
I changed MAXCLIENTS from 512 to 2048 so I could get some 'worst case'
measurements. I figured x11perf -noop would be a nice test, and then
when I saw what the 'Sync time adjustment' was in these situations, I
wondered what x11perf -noop -sync would do and was surprised to see that
the effect was even larger. Clearly, calling poll with thousands of file
descriptors is expensive...
-noop -noop -sync
1 505 2047 1 505 2047
epoll 53e6 53e6 53e6 140e3 140e3 140e3
poll 53e6 50e6 34e6 140e3 12e3 2e3
select 43e6 43e6 140e3 12e3
So, epoll clearly wins when we have a bunch of clients, but both poll
and epoll are winning over select because we aren't sending 512 file
descriptors into the kernel for it to mull over every time we call
I want to clean up the patches on my epoll branch before trying to get
them merged; there are a couple of false starts left in the branch
before I figured out the interface I wanted.
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