Messages in this thread | | | From | Daniel Axtens <> | Subject | Re: [PATCH] fs/select.c: batch user writes in do_sys_poll | Date | Thu, 13 Aug 2020 21:36:52 +1000 |
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Hi,
>> Seem like this could simply use a copy_to_user to further simplify >> things? > > I'll benchmark it and find out.
I tried this:
for (walk = head; walk; walk = walk->next) { - struct pollfd *fds = walk->entries; - int j; - - for (j = 0; j < walk->len; j++, ufds++) - if (__put_user(fds[j].revents, &ufds->revents)) - goto out_fds; + if (copy_to_user(ufds, walk->entries, + sizeof(struct pollfd) * walk->len)) + goto out_fds; + ufds += walk->len; }
With that approach, the poll2 microbenchmark (which polls 128 fds) is about as fast as v1.
However, the poll1 microbenchmark, which polls just 1 fd, regresses a touch (<1% - ~2%) compared to the current code, although it's largely within the noise. Thoughts?
Kind regards, Daniel
>> Also please don't pointlessly add overly long lines. > > Weird, I ran the commit through checkpatch and it didn't pick it > up. I'll check the next version more carefully. > > Regards, > Daniel
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