Messages in this thread | | | Date | Thu, 28 Feb 2008 14:13:10 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] Prevent the loop in timespec_add_ns() to be optimised away |
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On Thu, 28 Feb 2008 22:58:49 +0100 (CET) Thomas Gleixner <tglx@linutronix.de> wrote:
> On Wed, 27 Feb 2008, Andrew Morton wrote: > > > On Fri, 22 Feb 2008 22:40:45 +0100 > > Segher Boessenkool <segher@kernel.crashing.org> wrote: > > > > > ...since some architectures don't support __udivdi3() (and > > > we don't want to use that, anyway). > > > > > > Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org> > > > --- > > > include/linux/time.h | 4 ++++ > > > 1 files changed, 4 insertions(+), 0 deletions(-) > > > > > > diff --git a/include/linux/time.h b/include/linux/time.h > > > index 2091a19..d32ef0a 100644 > > > --- a/include/linux/time.h > > > +++ b/include/linux/time.h > > > @@ -174,6 +174,10 @@ static inline void timespec_add_ns(struct timespec *a, u64 ns) > > > { > > > ns += a->tv_nsec; > > > while(unlikely(ns >= NSEC_PER_SEC)) { > > > + /* The following asm() prevents the compiler from > > > + * optimising this loop into a modulo operation. */ > > > + asm("" : "+r"(ns)); > > > + > > > ns -= NSEC_PER_SEC; > > > a->tv_sec++; > > > } > > > > It's pretty sad that we need to turn this into a loop just because of the > > __udivdi3() thing. > > > > otoh, it's rarely occurring, and it could be that the number of times it > > loops is usually 1 (if it wasn't zero), so perhaps a loop is faster than a > > divide anyway. > > > > This code is probably too large to be inlined. > > > > I queued this patch as needed-in-2.6.25, to-be-merged-via-Thomas. > > Are you going to send it or should I grab it from the mailing list > myself ? >
My secret-undocumented protocol for handling a patch which I think is needed in 2.6.current and which is handled via a subsystem tree is:
- queue it up behind all the subsystem trees in -mm's "2.6.25:" section
- actually it's now "2.6.25"'s "others:" section. I've split the "2.6.25:" section into two parts: "me:" and "others:".
- drop it if it turns up in a subsystem tree
- and hope like hell that whoever merged it has considered whether it's needed in the current kernel cycle, because I just lost track of it.
- let it cook for a few days or more, to give time for people to comment, and perhaps to get it into a -mm release
- send it out to the subsystem maintainer tagged as "[patch (for 2.6.25?)]"
- repeat.
patches which I currently have in this state are:
x86-cast-cmpxchg-and-cmpxchg_local-result-for-386-and-486.patch x86-fix-clearcopy_user_page-declarations-in-pageh.patch x86-visws-fix-printk-format-warnings.patch mpt-fusion-dont-oops-if-numphys==0.patch bluetooth-hci_core-defer-hci_unregister_sysfs.patch e100-do-suspend-shutdown-like-e1000.patch dm-raid1-bitops-bug.patch iova-lockdep-false-alarm-fix.patch bluetooth-conwise-technology-based-adapters-with-buggy-sco-support-bugzilla-9027.patch ieee80211-fix-broken-error-handling-in-ieee80211_sta_process_addba_request.patch fix-typo-in-tick-broadcastc.patch i8042-use-sgi_has_i8042-to-select-sgi-i8042-handlinig.patch fix-b43-driver-build-for-arm.patch apanel-fix-kconfig-dependencies.patch de2104x-remove-bug_on-when-changing-media-type.patch scsi-fix-cd-burning-regression.patch arm-fix-freeing-of-page-tables-in-free_pgd_slow.patch time-prevent-the-loop-in-timespec_add_ns-from-being-optimised-away.patch acpi-ec-fix-regression.patch drivers-acpi-asus_acpic-correct-use-of-and.patch drivers-media-video-em28xx-correct-use-of-and.patch drivers-media-video-em28xx-correct-use-of-and-fix.patch drivers-net-wireless-iwlwifi-iwl-4965c-correct-use-of-and.patch time-dont-touch-an-offlined-cpus-ts-tick_stopped-in-tick_cancel_sched_timer.patch scsi-arcmsr-update-driver-version.patch
the way to stop me from continuing to loop is to send me an "acked-by, please send to Linus for 2.6.25".
I'll then move the patch into -mm's "me:" section (or even right up next to origin.patch if it's simple-and-obvious) for sending to LT.
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