mirror of
https://github.com/torvalds/linux.git
synced 2026-07-18 11:37:36 +02:00
64c7c8f885
Make some changes to the NEED_RESCHED and POLLING_NRFLAG to reduce confusion, and make their semantics rigid. Improves efficiency of resched_task and some cpu_idle routines. * In resched_task: - TIF_NEED_RESCHED is only cleared with the task's runqueue lock held, and as we hold it during resched_task, then there is no need for an atomic test and set there. The only other time this should be set is when the task's quantum expires, in the timer interrupt - this is protected against because the rq lock is irq-safe. - If TIF_NEED_RESCHED is set, then we don't need to do anything. It won't get unset until the task get's schedule()d off. - If we are running on the same CPU as the task we resched, then set TIF_NEED_RESCHED and no further action is required. - If we are running on another CPU, and TIF_POLLING_NRFLAG is *not* set after TIF_NEED_RESCHED has been set, then we need to send an IPI. Using these rules, we are able to remove the test and set operation in resched_task, and make clear the previously vague semantics of POLLING_NRFLAG. * In idle routines: - Enter cpu_idle with preempt disabled. When the need_resched() condition becomes true, explicitly call schedule(). This makes things a bit clearer (IMO), but haven't updated all architectures yet. - Many do a test and clear of TIF_NEED_RESCHED for some reason. According to the resched_task rules, this isn't needed (and actually breaks the assumption that TIF_NEED_RESCHED is only cleared with the runqueue lock held). So remove that. Generally one less locked memory op when switching to the idle thread. - Many idle routines clear TIF_POLLING_NRFLAG, and only set it in the inner most polling idle loops. The above resched_task semantics allow it to be set until before the last time need_resched() is checked before going into a halt requiring interrupt wakeup. Many idle routines simply never enter such a halt, and so POLLING_NRFLAG can be always left set, completely eliminating resched IPIs when rescheduling the idle task. POLLING_NRFLAG width can be increased, to reduce the chance of resched IPIs. Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Ingo Molnar <mingo@elte.hu> Cc: Con Kolivas <kernel@kolivas.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> |
||
|---|---|---|
| .. | ||
| vdso32 | ||
| vdso64 | ||
| align.c | ||
| asm-offsets.c | ||
| btext.c | ||
| cpu_setup_power4.S | ||
| dma.c | ||
| eeh.c | ||
| firmware.c | ||
| head.S | ||
| hvconsole.c | ||
| hvcserver.c | ||
| idle.c | ||
| ioctl32.c | ||
| iomap.c | ||
| iommu.c | ||
| irq.c | ||
| kprobes.c | ||
| lparcfg.c | ||
| machine_kexec.c | ||
| Makefile | ||
| misc.S | ||
| module.c | ||
| nvram.c | ||
| pacaData.c | ||
| pci_direct_iommu.c | ||
| pci_dn.c | ||
| pci_iommu.c | ||
| pci.c | ||
| ppc_ksyms.c | ||
| proc_ppc64.c | ||
| prom_init.c | ||
| prom.c | ||
| rtas_pci.c | ||
| rtc.c | ||
| scanlog.c | ||
| semaphore.c | ||
| sysfs.c | ||
| udbg_16550.c | ||
| udbg_scc.c | ||
| udbg.c | ||
| vdso.c | ||
| vmlinux.lds.S | ||