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| author | Rusty Russell <rusty@rustcorp.com.au> | 2012-08-06 11:59:49 +0400 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2018-02-13 21:32:14 +0300 |
| commit | 0ed38b9005b4d959baa7a454e8e81784488b3a49 (patch) | |
| tree | 17a6ae3acc543ffd7e35f4e08d496def0fcc6c3d /Documentation | |
| parent | 0a8896d4a278033a7e860cfd43da0ade04b2ef48 (diff) | |
| download | linux-0ed38b9005b4d959baa7a454e8e81784488b3a49.tar.xz | |
x86/smp: Don't ever patch back to UP if we unplug cpus
commit 816afe4ff98ee10b1d30fd66361be132a0a5cee6 upstream.
We still patch SMP instructions to UP variants if we boot with a
single CPU, but not at any other time. In particular, not if we
unplug CPUs to return to a single cpu.
Paul McKenney points out:
mean offline overhead is 6251/48=130.2 milliseconds.
If I remove the alternatives_smp_switch() from the offline
path [...] the mean offline overhead is 550/42=13.1 milliseconds
Basically, we're never going to get those 120ms back, and the
code is pretty messy.
We get rid of:
1) The "smp-alt-once" boot option. It's actually "smp-alt-boot", the
documentation is wrong. It's now the default.
2) The skip_smp_alternatives flag used by suspend.
3) arch_disable_nonboot_cpus_begin() and arch_disable_nonboot_cpus_end()
which were only used to set this one flag.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul McKenney <paul.mckenney@us.ibm.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/87vcgwwive.fsf@rustcorp.com.au
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/kernel-parameters.txt | 3 |
1 files changed, 0 insertions, 3 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index ccaf4be39d17..0d27ce60d452 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2440,9 +2440,6 @@ bytes respectively. Such letter suffixes can also be entirely omitted. smart2= [HW] Format: <io1>[,<io2>[,...,<io8>]] - smp-alt-once [X86-32,SMP] On a hotplug CPU system, only - attempt to substitute SMP alternatives once at boot. - smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port smsc-ircc2.ircc_sir= [HW] SIR base I/O port |