[tip:x86/cleanups] x86/cpuid: Allow cpuid_read() to schedule

[tip-bot for Eric Dumazet]

Commit-ID:  67bbd7a8d6bcdc44cc27105ae8c374e9176ceaf1
Gitweb: https://git.kernel.org/tip/67bbd7a8d6bcdc44cc27105ae8c374e9176ceaf1
Author: Eric Dumazet 
AuthorDate: Fri, 23 Mar 2018 14:58:18 -0700
Committer:  Thomas Gleixner 
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 
Signed-off-by: Thomas Gleixner 
Acked-by: Ingo Molnar 
Cc: Hugh Dickins 
Cc: Borislav Petkov 
Cc: Eric Dumazet 
Link: https://lkml.kernel.org/r/20180323215818.127774-2-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 
 #include 
 #include 
+#include 
 
 #include 
 #include 
@@ -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,
+   >regs.eax, >regs.ebx,
+   >regs.ecx, >regs.edx);
 
-   cpuid_count(cmd->eax, cmd->ecx,
-   >eax, >ebx, >ecx, >edx);
+   complete(>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();
for (; count; count -= 16) {
-   cmd.eax = pos;
-   cmd.ecx = pos >> 32;
-   err = smp_call_function_single(cpu, cpuid_smp_cpuid, , 1);
+   call_single_data_t csd = {
+   .func = cpuid_smp_cpuid,
+   .info = ,
+   };
+
+   cmd.regs.eax = pos;
+   cmd.regs.ecx = pos >> 32;
+
+   err = smp_call_function_single_async(cpu, );
if (err)
break;
-   if (copy_to_user(tmp, , 16)) {
+   wait_for_completion();
+   if (copy_to_user(tmp, , 16)) {
err = -EFAULT;
break;
}
tmp += 16;
bytes += 16;
*ppos = ++pos;
+   reinit_completion();
}
 
return bytes ? bytes : err;

[tip:x86/cleanups] x86/cpuid: Allow cpuid_read() to schedule

[tip-bot for Eric Dumazet]

Commit-ID:  67bbd7a8d6bcdc44cc27105ae8c374e9176ceaf1
Gitweb: https://git.kernel.org/tip/67bbd7a8d6bcdc44cc27105ae8c374e9176ceaf1
Author: Eric Dumazet 
AuthorDate: Fri, 23 Mar 2018 14:58:18 -0700
Committer:  Thomas Gleixner 
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 
Signed-off-by: Thomas Gleixner 
Acked-by: Ingo Molnar 
Cc: Hugh Dickins 
Cc: Borislav Petkov 
Cc: Eric Dumazet 
Link: https://lkml.kernel.org/r/20180323215818.127774-2-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 
 #include 
 #include 
+#include 
 
 #include 
 #include 
@@ -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,
+   >regs.eax, >regs.ebx,
+   >regs.ecx, >regs.edx);
 
-   cpuid_count(cmd->eax, cmd->ecx,
-   >eax, >ebx, >ecx, >edx);
+   complete(>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();
for (; count; count -= 16) {
-   cmd.eax = pos;
-   cmd.ecx = pos >> 32;
-   err = smp_call_function_single(cpu, cpuid_smp_cpuid, , 1);
+   call_single_data_t csd = {
+   .func = cpuid_smp_cpuid,
+   .info = ,
+   };
+
+   cmd.regs.eax = pos;
+   cmd.regs.ecx = pos >> 32;
+
+   err = smp_call_function_single_async(cpu, );
if (err)
break;
-   if (copy_to_user(tmp, , 16)) {
+   wait_for_completion();
+   if (copy_to_user(tmp, , 16)) {
err = -EFAULT;
break;
}
tmp += 16;
bytes += 16;
*ppos = ++pos;
+   reinit_completion();
}
 
return bytes ? bytes : err;