Messages in this thread | | | Subject | Re: [PATCH 2/2] x86/speculation: switch_to_cond_stibp on is the likely case | From | Waiman Long <> | Date | Thu, 6 Dec 2018 10:38:00 -0500 |
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On 12/06/2018 03:41 AM, Peter Zijlstra wrote: > On Wed, Dec 05, 2018 at 02:49:28PM -0500, Waiman Long wrote: >> Since conditional STIBP is the default, it should be treated as >> the likely case. Changes the use of static_branch_unlikely() to >> static_branch_likely() for switch_to_cond_stibp. > So now you're making kernels on 'fixed' or unaffected hardware slower.
Good point.
The reason I sent out this patch is because of the inconsistency in the use of likely/unlikely hints.
arch/x86/kernel/cpu/bugs.c:156: if (static_branch_unlikely(&switch_to_cond_stibp)) arch/x86/kernel/process.c:440: static_branch_unlikely(&switch_to_cond_stibp)) { arch/x86/kernel/process.h:26: if (!static_branch_likely(&switch_to_cond_stibp)) {
So if we are aiming to optimize for "fixed" or unaffected hardware, maybe we should modify the likely hint to unlikely then.
Cheers, Longman
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