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xen-devel
[Xen-devel] Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT
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To: |
"H. Peter Anvin" <hpa@xxxxxxxxx> |
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Subject: |
[Xen-devel] Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT |
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From: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
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Date: |
Thu, 22 Jan 2009 16:08:15 -0800 |
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Cc: |
Zachary Amsden <zach@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "jeremy@xxxxxxxxxxxxx" <jeremy@xxxxxxxxxxxxx>, "rusty@xxxxxxxxxxxxxxx" <rusty@xxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, "chrisw@xxxxxxxxxxxx" <chrisw@xxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> |
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Thu, 22 Jan 2009 16:08:47 -0800 |
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<20090120110542.GE19505@xxxxxxxxxxxxx> <20090120112634.GA20858@xxxxxxx> <20090120140324.GA26424@xxxxxxx> <49763806.5090009@xxxxxxxx> <20090120205653.GA19710@xxxxxxx> <20090121072718.GN24891@xxxxxxxxxxxxx> <4977A051.8050203@xxxxxxxx> <1232663311.16317.176.camel@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <4978F6C6.3090003@xxxxxxxx> <4978F7DC.1040503@xxxxxxxxx> <1232665120.16317.186.camel@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <497906A4.2030008@xxxxxxxxx> |
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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.
J
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