Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT

From: Jeremy Fitzhardinge
Date: Thu Jan 22 2009 - 19:08:31 EST

H. Peter Anvin wrote:
Right now a number of the call sites contain a huge push/pop sequence followed by an indirect call. We can patch in the native code to avoid the branch overhead, but the register constraints and icache footprint is unchanged.

That's true for the pvops hooks emitted in the .S files, but not so true for ones in C code (well, there are no explicit push/pops, but the presence of the call may cause the compiler to generate them).

The .S hooks can definitely be cleaned up, but I don't think that's germane to Nick's observations that the mm code is showing slowdowns.

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