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[Xen-devel] vsyscalls may be going away... impact on Xen time performanc

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] vsyscalls may be going away... impact on Xen time performance on Linux in the future?
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Thu, 9 Jun 2011 14:55:16 -0700 (PDT)
Cc: jeremy@xxxxxxxx, Konrad Wilk <konrad.wilk@xxxxxxxxxx>
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It appears that Xen time mechanisms that use vsyscall may be
getting slower...

"This is a significant performance penalty (~220ns here) for
all vsyscall users, but there aren't many left."


I honestly don't remember all the details myself anymore,
but I think this means that user apps in Xen PV domains
that call gettimeofday a *lot* may be in for a bit of
a shock when they move to a 3.x kernel in the future.
(Many enterprise apps do things like timestamp transactions,
which can lead to 10s of thousands of gettimeofday's
per second.)

See the xen-devel discussion here:



P.S. For lwn subscribers (or non-subscribers willing to wait a week),
see Jonathan Corbet's nice overview at http://lwn.net/Articles/446125/ 


Thanks... for the memory!
I really could use more / my throughput's on the floor
The balloon is flat / my swap disk's fat / I've OOM's in store
Overcommitted so much
(with apologies to Bob Hope)

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