summaryrefslogtreecommitdiff
path: root/arch/x86/kernel/cpuid.c
diff options
context:
space:
mode:
authorEric Dumazet <edumazet@google.com>2018-03-24 00:58:18 +0300
committerThomas Gleixner <tglx@linutronix.de>2018-03-27 13:01:48 +0300
commit67bbd7a8d6bcdc44cc27105ae8c374e9176ceaf1 (patch)
treeaa876adde482382ffae7c3447a3179f9afde385d /arch/x86/kernel/cpuid.c
parent07cde313b2d21f728cec2836db7cdb55476f7a26 (diff)
downloadlinux-67bbd7a8d6bcdc44cc27105ae8c374e9176ceaf1.tar.xz
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 <edumazet@google.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Ingo Molnar <mingo@kernel.org> Cc: Hugh Dickins <hughd@google.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Eric Dumazet <eric.dumazet@gmail.com> Link: https://lkml.kernel.org/r/20180323215818.127774-2-edumazet@google.com
Diffstat (limited to 'arch/x86/kernel/cpuid.c')
-rw-r--r--arch/x86/kernel/cpuid.c34
1 files 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;