On Tue, 27 Nov 2007, Andrew Morton wrote:
> On Tue, 27 Nov 2007 12:47:46 -0800 (PST)
> Davide Libenzi <[email protected]> wrote:
>
> > On Tue, 27 Nov 2007, Andrew Morton wrote:
> >
> > > On Sun, 25 Nov 2007 14:14:19 -0800 Davide Libenzi <[email protected]> wrote:
> > >
> > > > +static struct file *timerfd_fget(int fd)
> > > > +{
> > > > + struct file *file;
> > > > +
> > > > + file = fget(fd);
> > > > + if (!file)
> > > > + return ERR_PTR(-EBADF);
> > > > + if (file->f_op != &timerfd_fops) {
> > > > + fput(file);
> > > > + return ERR_PTR(-EINVAL);
> > > > + }
> > > > +
> > > > + return file;
> > > > +}
> > >
> > > I suppose we could use fget_light() in here sometime. It is significantly
> > > quicker in microbenchmarks. Or it was - nobody has checked that in a few
> > > years afaik.
> >
> > Should I now?
>
> No great rush. It'd be fun to see if it actually makes any measurable
> difference on modern hardware (hint ;)).
I was going to say BS, given that at the time of the tests, the files
struct was protected by an rwlock whereas now there's a rcu one.
But that seems not the case:
http://www.xmailserver.org/fget-light-test.c
$ fget-light-test -r 900000000
warming up ...
testing non-shared ...
time = 314.354000 ms
testing shared ...
time = 390.781000 ms
And here is the oprofile output:
[SHARED CASE]
samples % app name symbol name
7436 28.9339 vmlinux __clear_user
2369 9.2179 vmlinux system_call
1710 6.6537 vmlinux fget_light
1244 4.8405 vmlinux inotify_dentry_parent_queue_event
1128 4.3891 vmlinux sys_read
1041 4.0506 libpthread-2.6.1.so __read_nocancel
1027 3.9961 Xorg (no symbols)
978 3.8054 vmlinux read_zero
755 2.9377 vmlinux vfs_read
545 2.1206 vmlinux inotify_inode_queue_event
507 1.9728 vmlinux sysret_check
414 1.6109 vmlinux rw_verify_area
405 1.5759 vmlinux unix_poll
371 1.4436 nvidia (no symbols)
333 1.2957 vmlinux acpi_pm_read
311 1.2101 nvidia_drv.so (no symbols)
290 1.1284 vmlinux do_select
288 1.1206 vmlinux dnotify_parent
253 0.9844 libc-2.6.1.so (no symbols)
232 0.9027 bash (no symbols)
216 0.8405 libpthread-2.6.1.so __pthread_enable_asynccancel
[UNSHARED CASE]
samples % app name symbol name
6542 27.6922 vmlinux __clear_user
4074 17.2452 vmlinux vfs_read
1266 5.3590 vmlinux inotify_inode_queue_event
1091 4.6182 Xorg (no symbols)
1059 4.4827 vmlinux system_call
937 3.9663 libpthread-2.6.1.so __read_nocancel
544 2.3027 vmlinux clear_user
484 2.0488 vmlinux dnotify_parent
445 1.8837 vmlinux read_zero
438 1.8540 vmlinux sysret_check
414 1.7525 vmlinux unix_poll
407 1.7228 nvidia (no symbols)
389 1.6466 vmlinux acpi_pm_read
315 1.3334 nvidia_drv.so (no symbols)
312 1.3207 vmlinux inotify_dentry_parent_queue_event
312 1.3207 vmlinux sys_read
305 1.2911 vmlinux rw_verify_area
304 1.2868 vmlinux do_select
222 0.9397 libc-2.6.1.so (no symbols)
214 0.9059 bash (no symbols)
196 0.8297 fget-light-test read_test
185 0.7831 vmlinux fget_light
You can clearly notice the fget_light() drop out of the relevance window.
BTW, are all those "notify" noises supposed to be there?
- Davide
-
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