x86/apic: Remove pointless fence in lapic_next_deadline()

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lapic_next_deadline() contains a fence before the TSC read and the write to
the TSC_DEADLINE MSR with a content free and therefore useless comment:

    /* This MSR is special and need a special fence: */

The MSR is not really special. It is just not a serializing MSR, but that
does not matter at all in this context as all of these operations are
strictly CPU local.

The only thing the fence prevents is that the RDTSC is speculated ahead,
but that's not really relevant as the delta is calculated way before based
on a previous TSC read and therefore inaccurate by definition.

So removing the fence is just making it slightly more inaccurate in the
worst case, but that is irrelevant as it's way below the actual system
immanent latencies and variations.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163429.809059527@kernel.org

...

This commit is contained in:

Thomas Gleixner 2026-02-24 17:36:29 +01:00 • committed by Peter Zijlstra

parent b27801189f

commit 92d0e753d5

1 changed files with 7 additions and 9 deletions

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arch/x86/kernel/apic/apic.c

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