Commit-ID: 67bbd7a8d6bcdc44cc27105ae8c374e9176ceaf1 Gitweb: https://git.kernel.org/tip/67bbd7a8d6bcdc44cc27105ae8c374e9176ceaf1 Author: Eric Dumazet <eduma...@google.com> AuthorDate: Fri, 23 Mar 2018 14:58:18 -0700 Committer: Thomas Gleixner <t...@linutronix.de> CommitDate: Tue, 27 Mar 2018 12:01:48 +0200
x86/cpuid: Allow cpuid_read() to schedule High latencies can be observed caused by a daemon periodically reading CPUID on all cpus. On KASAN enabled kernels ~10ms latencies can be observed. 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. cpuid_read() is invoked in preemptible context, so it can be converted to sleep instead of busy wait. Switching to smp_call_function_single_async() and a completion allows to reschedule and reduces CPU usage and latencies. Signed-off-by: Eric Dumazet <eduma...@google.com> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Acked-by: Ingo Molnar <mi...@kernel.org> Cc: Hugh Dickins <hu...@google.com> Cc: Borislav Petkov <b...@alien8.de> Cc: Eric Dumazet <eric.duma...@gmail.com> Link: https://lkml.kernel.org/r/20180323215818.127774-2-eduma...@google.com --- arch/x86/kernel/cpuid.c | 34 ++++++++++++++++++++++++++-------- 1 file changed, 26 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/cpuid.c b/arch/x86/kernel/cpuid.c index 0931a105ffe1..1d300f96df4b 100644 --- a/arch/x86/kernel/cpuid.c +++ b/arch/x86/kernel/cpuid.c @@ -40,6 +40,7 @@ #include <linux/notifier.h> #include <linux/uaccess.h> #include <linux/gfp.h> +#include <linux/completion.h> #include <asm/processor.h> #include <asm/msr.h> @@ -47,19 +48,27 @@ static struct class *cpuid_class; static enum cpuhp_state cpuhp_cpuid_state; +struct cpuid_regs_done { + struct cpuid_regs regs; + struct completion done; +}; + static void cpuid_smp_cpuid(void *cmd_block) { - struct cpuid_regs *cmd = (struct cpuid_regs *)cmd_block; + struct cpuid_regs_done *cmd = cmd_block; + + cpuid_count(cmd->regs.eax, cmd->regs.ecx, + &cmd->regs.eax, &cmd->regs.ebx, + &cmd->regs.ecx, &cmd->regs.edx); - cpuid_count(cmd->eax, cmd->ecx, - &cmd->eax, &cmd->ebx, &cmd->ecx, &cmd->edx); + complete(&cmd->done); } static ssize_t cpuid_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) { char __user *tmp = buf; - struct cpuid_regs cmd; + struct cpuid_regs_done cmd; int cpu = iminor(file_inode(file)); u64 pos = *ppos; ssize_t bytes = 0; @@ -68,19 +77,28 @@ static ssize_t cpuid_read(struct file *file, char __user *buf, if (count % 16) return -EINVAL; /* Invalid chunk size */ + init_completion(&cmd.done); for (; count; count -= 16) { - cmd.eax = pos; - cmd.ecx = pos >> 32; - err = smp_call_function_single(cpu, cpuid_smp_cpuid, &cmd, 1); + call_single_data_t csd = { + .func = cpuid_smp_cpuid, + .info = &cmd, + }; + + cmd.regs.eax = pos; + cmd.regs.ecx = pos >> 32; + + err = smp_call_function_single_async(cpu, &csd); if (err) break; - if (copy_to_user(tmp, &cmd, 16)) { + wait_for_completion(&cmd.done); + if (copy_to_user(tmp, &cmd.regs, 16)) { err = -EFAULT; break; } tmp += 16; bytes += 16; *ppos = ++pos; + reinit_completion(&cmd.done); } return bytes ? bytes : err;
