Re: [PATCH] x86: Add clflush before monitor for Intel 7400 series

From: H. Peter Anvin
Date: Fri Oct 17 2008 - 16:13:49 EST

Pallipadi, Venkatesh wrote:


Do you still have reservations about this being expensive.
Note that this is only done when a CPU is about to go idle and
The cost of clflush itself will be minimal compared to idle
entry + idle exit latency.

I guess I'm a bit confused about the tradeoff of CLFLUSH versus simply disabling MWAIT. This is a relatively recent processor and so optimizing matters (if this was a P4 I would be more worried about what has least impact on the kernel as a whole.)

Entry and exit latency do matter (specifically, exit latency matters for longer waits and the combined entry+exit latency matters for short waits.)

On the other hand, perhaps what we need to do is to get the fix in and worry about performance later.

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