Messages in this thread Patch in this message | | | Date | Wed, 04 Jan 2006 00:07:19 +0100 | From | Eric Dumazet <> | Subject | Re: [PATCH] [RFC] Optimize select/poll by putting small data sets on the stack |
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Eric Dumazet a écrit : > Andi Kleen a écrit : >> This is a RFC for now. I would be interested in testing >> feedback. Patch is for 2.6.15. >> >> Optimize select and poll by a using stack space for small fd sets >> >> This brings back an old optimization from Linux 2.0. Using >> the stack is faster than kmalloc. On a Intel P4 system >> it speeds up a select of a single pty fd by about 13% >> (~4000 cycles -> ~3500) > > Was this result on UP or SMP kernel ? Preempt or not ? > > I think we might play in do_pollfd() and use fget_light()/fput_light() > instead of fget()/fput() that are somewhat expensive because of atomic > inc/dec on SMP. >
Just for completeness I include this patch against 2.6.15
--- linux-2.6.15/fs/select.c 2006-01-03 04:21:10.000000000 +0100 +++ linux-2.6.15-ed/fs/select.c 2006-01-04 00:04:10.000000000 +0100 @@ -221,17 +221,18 @@ } for (j = 0; j < __NFDBITS; ++j, ++i, bit <<= 1) { + int fput_needed; if (i >= n) break; if (!(bit & all_bits)) continue; - file = fget(i); + file = fget_light(i, &fput_needed); if (file) { f_op = file->f_op; mask = DEFAULT_POLLMASK; if (f_op && f_op->poll) mask = (*f_op->poll)(file, retval ? NULL : wait); - fput(file); + fput_light(file, fput_needed); if ((mask & POLLIN_SET) && (in & bit)) { res_in |= bit; retval++; @@ -417,14 +418,15 @@ fdp = fdpage+i; fd = fdp->fd; if (fd >= 0) { - struct file * file = fget(fd); + int fput_needed; + struct file * file = fget_light(fd, &fput_needed); mask = POLLNVAL; if (file != NULL) { mask = DEFAULT_POLLMASK; if (file->f_op && file->f_op->poll) mask = file->f_op->poll(file, *pwait); mask &= fdp->events | POLLERR | POLLHUP; - fput(file); + fput_light(file, fput_needed); } if (mask) { *pwait = NULL; | |