From 07cde313b2d21f728cec2836db7cdb55476f7a26 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 23 Mar 2018 14:58:17 -0700 Subject: x86/msr: Allow rdmsr_safe_on_cpu() to schedule High latencies can be observed caused by a daemon periodically reading various MSR on all cpus. On KASAN enabled kernels ~10ms latencies can be observed simply reading one MSR. Even without KASAN, sending an IPI to a CPU, which is in a deep sleep state or in a long hard IRQ disabled section, waiting for the answer can consume hundreds of microseconds. All usage sites are in preemptible context, convert rdmsr_safe_on_cpu() to use a completion instead of busy polling. Overall daemon cpu usage was reduced by 35 %, and latencies caused by msr_read() disappeared. Signed-off-by: Eric Dumazet Signed-off-by: Thomas Gleixner Acked-by: Ingo Molnar Cc: Hugh Dickins Cc: Borislav Petkov Cc: Eric Dumazet Link: https://lkml.kernel.org/r/20180323215818.127774-1-edumazet@google.com --- arch/x86/lib/msr-smp.c | 32 ++++++++++++++++++++++++-------- 1 file changed, 24 insertions(+), 8 deletions(-) (limited to 'arch/x86/lib') diff --git a/arch/x86/lib/msr-smp.c b/arch/x86/lib/msr-smp.c index 693cce0..761ba06 100644 --- a/arch/x86/lib/msr-smp.c +++ b/arch/x86/lib/msr-smp.c @@ -2,6 +2,7 @@ #include #include #include +#include #include static void __rdmsr_on_cpu(void *info) @@ -143,13 +144,19 @@ void wrmsr_on_cpus(const struct cpumask *mask, u32 msr_no, struct msr *msrs) } EXPORT_SYMBOL(wrmsr_on_cpus); +struct msr_info_completion { + struct msr_info msr; + struct completion done; +}; + /* These "safe" variants are slower and should be used when the target MSR may not actually exist. */ static void __rdmsr_safe_on_cpu(void *info) { - struct msr_info *rv = info; + struct msr_info_completion *rv = info; - rv->err = rdmsr_safe(rv->msr_no, &rv->reg.l, &rv->reg.h); + rv->msr.err = rdmsr_safe(rv->msr.msr_no, &rv->msr.reg.l, &rv->msr.reg.h); + complete(&rv->done); } static void __wrmsr_safe_on_cpu(void *info) @@ -161,17 +168,26 @@ static void __wrmsr_safe_on_cpu(void *info) int rdmsr_safe_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h) { + struct msr_info_completion rv; + call_single_data_t csd = { + .func = __rdmsr_safe_on_cpu, + .info = &rv, + }; int err; - struct msr_info rv; memset(&rv, 0, sizeof(rv)); + init_completion(&rv.done); + rv.msr.msr_no = msr_no; - rv.msr_no = msr_no; - err = smp_call_function_single(cpu, __rdmsr_safe_on_cpu, &rv, 1); - *l = rv.reg.l; - *h = rv.reg.h; + err = smp_call_function_single_async(cpu, &csd); + if (!err) { + wait_for_completion(&rv.done); + err = rv.msr.err; + } + *l = rv.msr.reg.l; + *h = rv.msr.reg.h; - return err ? err : rv.err; + return err; } EXPORT_SYMBOL(rdmsr_safe_on_cpu); -- cgit v1.1 From 9b9a51354cae933f5640b5bb73bbcd32f989122f Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 27 Mar 2018 20:22:33 -0700 Subject: x86/msr: Make rdmsrl_safe_on_cpu() scheduling safe as well When changing rdmsr_safe_on_cpu() to schedule, it was missed that __rdmsr_safe_on_cpu() was also used by rdmsrl_safe_on_cpu() Make rdmsrl_safe_on_cpu() a wrapper instead of copy/pasting the code which was added for the completion handling. Fixes: 07cde313b2d2 ("x86/msr: Allow rdmsr_safe_on_cpu() to schedule") Reported-by: kbuild test robot Signed-off-by: Eric Dumazet Signed-off-by: Thomas Gleixner Cc: Borislav Petkov Cc: Eric Dumazet Cc: "H. Peter Anvin" Link: https://lkml.kernel.org/r/20180328032233.153055-1-edumazet@google.com --- arch/x86/lib/msr-smp.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) (limited to 'arch/x86/lib') diff --git a/arch/x86/lib/msr-smp.c b/arch/x86/lib/msr-smp.c index 761ba06..fee8b9c 100644 --- a/arch/x86/lib/msr-smp.c +++ b/arch/x86/lib/msr-smp.c @@ -225,16 +225,13 @@ EXPORT_SYMBOL(wrmsrl_safe_on_cpu); int rdmsrl_safe_on_cpu(unsigned int cpu, u32 msr_no, u64 *q) { + u32 low, high; int err; - struct msr_info rv; - memset(&rv, 0, sizeof(rv)); + err = rdmsr_safe_on_cpu(cpu, msr_no, &low, &high); + *q = (u64)high << 32 | low; - rv.msr_no = msr_no; - err = smp_call_function_single(cpu, __rdmsr_safe_on_cpu, &rv, 1); - *q = rv.reg.q; - - return err ? err : rv.err; + return err; } EXPORT_SYMBOL(rdmsrl_safe_on_cpu); -- cgit v1.1