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x86, microcode: Don't request microcode from userspace unnecessarily

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Requesting the microcode from userspace *every time* when onlining CPUs
(during a CPU hotplug operation) is unnecessary. Thus, ensure that
once the kernel gets the microcode after booting, it is not freed nor
invalidated when a CPU goes offline, so that it can be reused when that
CPU comes back online, without requesting userspace for it again. As a
result, the CPU hotplug operations become faster as well.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Link: http://lkml.kernel.org/r/4E91F908.5010006@linux.vnet.ibm.com
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
This commit is contained in:
Srivatsa S. Bhat 2011-10-09 15:42:00 -04:00 committed by Borislav Petkov
parent 37cf95162a
commit 70989449da
1 changed files with 7 additions and 1 deletions
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8
arch/x86/kernel/microcode_core.c
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@ -483,7 +483,13 @@ mc_cpu_callback(struct notifier_block *nb, unsigned long action, void *hcpu)
sysfs_remove_group(&sys_dev->kobj, &mc_attr_group);
pr_debug("CPU%d removed\n", cpu);
break;
case CPU_DEAD:
/*
* When a CPU goes offline, don't free up or invalidate the copy of
* the microcode in kernel memory, so that we can reuse it when the
* CPU comes back online without unnecessarily requesting the userspace
* for it again.
*/
case CPU_UP_CANCELED_FROZEN:
/* The CPU refused to come up during a system resume */
microcode_fini_cpu(cpu);