Peter Zijlstra <pet...@infradead.org> writes: > Subject: sched: Revert need_resched() to look at TIF_NEED_RESCHED > From: Peter Zijlstra <pet...@infradead.org> > Date: Fri Sep 27 17:20:30 CEST 2013 > > Yuanhan reported a serious throughput regression in his pigz > benchmark. Using the ftrace patch I found that several idle paths > need more TLC before we can switch the generic need_resched() over to > preempt_need_resched. > > The preemption paths benefit most from preempt_need_resched and do > indeed use it; all other need_resched() users don't really care that > much so reverting need_resched() back to tif_need_resched() is the > simple and safe solution. > > Reported-by: Yuanhan Liu <yuanhan....@linux.intel.com> > Signed-off-by: Peter Zijlstra <pet...@infradead.org>
I guess we still need to fix should_resched() I am hitting the below with upstream BUG: soft lockup - CPU#0 stuck for 23s! [qemu-system-ppc:4394] Modules linked in: CPU: 0 PID: 4394 Comm: qemu-system-ppc Not tainted 3.13.0-rc3+ #98 task: c0000001d0788400 ti: c0000001dca00000 task.ti: c0000001dca00000 NIP: c00000000082dd80 LR: c000000000081ae0 CTR: c000000000062ba0 REGS: c0000001dca02f70 TRAP: 0901 Not tainted (3.13.0-rc3+) MSR: 8000000000009032 <SF,EE,ME,IR,DR,RI> CR: 24822024 XER: 00000000 CFAR: c000000000081adc SOFTE: 1 GPR00: c000000000081ae0 c0000001dca031f0 c000000000d67ab0 0000000000000001 GPR04: 0000000071000002 0000000000000001 00000189a0d786b7 00000000018c0000 GPR08: 0000000000000001 0000000000000000 0000000000000000 c000000000da0000 GPR12: 0000000000000c00 c00000000fef0000 NIP [c00000000082dd80] ._cond_resched+0x0/0x40 LR [c000000000081ae0] .kvmppc_prepare_to_enter+0x2a0/0x2e0 Call Trace: [c0000001dca031f0] [c000000000081ae0] .kvmppc_prepare_to_enter+0x2a0/0x2e0 (unreliable) [c0000001dca03290] [c00000000008f2cc] .kvmppc_handle_exit_pr+0xec/0xa40 [c0000001dca03340] [c0000000000918c4] kvm_start_lightweight+0xac/0xbc [c0000001dca03510] [c00000000008efe0] .kvmppc_vcpu_run_pr+0x130/0x2a0 [c0000001dca039e0] [c0000000000855bc] .kvmppc_vcpu_run+0x2c/0x40 [c0000001dca03a50] [c000000000082c94] .kvm_arch_vcpu_ioctl_run+0x54/0x1b0 [c0000001dca03ae0] [c00000000007d5f8] .kvm_vcpu_ioctl+0x478/0x740 [c0000001dca03ca0] [c000000000218864] .do_vfs_ioctl+0x4a4/0x760 [c0000001dca03d80] [c000000000218b78] .SyS_ioctl+0x58/0xb0 [c0000001dca03e30] [c000000000009e58] syscall_exit+0x0/0x98 Instruction dump: e92d0260 e94911c0 812a0004 5529f07e 5529103e 912a0004 38210080 e8010010 ebc1fff0 ebe1fff8 7c0803a6 4e800020 <7c0802a6> 38600000 f8010010 f821ff91 The revert which Alexander tried had those http://mid.gmane.org/20131128132641.gp10...@twins.programming.kicks-ass.net > --- > arch/x86/include/asm/preempt.h | 8 -------- > include/asm-generic/preempt.h | 8 -------- > include/linux/sched.h | 5 +++++ > 3 files changed, 5 insertions(+), 16 deletions(-) > > --- a/arch/x86/include/asm/preempt.h > +++ b/arch/x86/include/asm/preempt.h > @@ -80,14 +80,6 @@ static __always_inline bool __preempt_co > } > > /* > - * Returns true when we need to resched -- even if we can not. > - */ > -static __always_inline bool need_resched(void) > -{ > - return unlikely(test_preempt_need_resched()); > -} > - > -/* > * Returns true when we need to resched and can (barring IRQ state). > */ > static __always_inline bool should_resched(void) > --- a/include/asm-generic/preempt.h > +++ b/include/asm-generic/preempt.h > @@ -85,14 +85,6 @@ static __always_inline bool __preempt_co > } > > /* > - * Returns true when we need to resched -- even if we can not. > - */ > -static __always_inline bool need_resched(void) > -{ > - return unlikely(test_preempt_need_resched()); > -} > - > -/* > * Returns true when we need to resched and can (barring IRQ state). > */ > static __always_inline bool should_resched(void) > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -2577,6 +2577,11 @@ static inline bool __must_check current_ > } > #endif > > +static __always_inline bool need_resched(void) > +{ > + return unlikely(tif_need_resched()); > +} > + > /* > * Thread group CPU time accounting. > */ -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
