hinting system for poll (was Re: /dev/poll vs. aio_)

Niels Provos (provos@citi.umich.edu)
Mon, 17 May 1999 15:59:30 -0400

In message <Pine.BSF.4.03.9905171010210.24425-100000@funky.monkey.org>, Chuck L
ever writes:
>Niels Provos is working on a "hinting" poll() for Linux that uses a system
>very similar to this where network devices register themselves with
>poll(), and provide hints when they are ready for I/O. Niels, maybe you
>can describe your work?
As part of the Linux Scalability Project I have implemented a hinting
system for poll to speed up network intensive applications, e.g. web
servers.

The hinting system works as follows:
The file descriptors are passed along as argument in the device
specific poll() call and the device driver keeps them in a backmapping
list. When an an event occurs that changes the poll state, the device
driver sets a hint for all file descriptors in the backmapping list.
At process wake up, the process only needs to call the device specific
poll() function for file descriptors that have a hint.

I have run a benchmark with thttpd-2.04 and httperf-0.6 between 2.2.3-ac4
and 2.2.3-ac4 + poll hinting. I obtained the following results for

readprofile -r
httperf --server localhost --port 8080 --num-conns 100000 --rate 650
readprofile | egrep "(poll|select|wait)" | sort -k3 -nr

2.2.3-ac4:
4017 do_select 6.9740
3024 sock_poll 75.6000
2521 inet_poll 57.2955
2344 tcp_poll 9.7667
375 sys_select 0.3189
187 __pollwait 0.9350
169 free_wait 1.0833
129 max_select_fd 0.7866
22 __tcp_select_window 0.1222

2.2.3-ac4-hint:
1460 do_select 1.5336
752 sys_select 0.6065
305 max_select_fd 1.3616
45 tcp_poll 0.1114
35 __tcp_select_window 0.1944
19 poll_free_wait 0.0651
15 sock_poll 0.3125
12 tcp_timewait_state_process 0.0435
10 expand_poll_hints 0.0128

They seem to indicate that the hinting system is able to avoid many
calls to {sock,inet,tcp}_poll. Perhaps somebody can explain to me how
comparable the output of readprofile is.

I am still working on this to make sure that it is bug free, but
at the moment I am fairly confident to make patches available
within about a week.

Greetings,
Niels.

--
Niels Provos <provos@citi.umich.edu> finger provos@umich.edu for pgp info


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/