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From: Dan Magenheimer <dan.magenheimer@oracle.com>
To: xen-devel@lists.xensource.com
Cc: jeremy@goop.org, Konrad Wilk <konrad.wilk@oracle.com>
Subject: vsyscalls may be going away... impact on Xen time performance on Linux in the future?
Date: Thu, 9 Jun 2011 14:55:16 -0700 (PDT)	[thread overview]
Message-ID: <070733f8-c7aa-4543-85dd-d353088b0e20@default> (raw)

Hmmm...

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."

http://lwn.net/Articles/446220/ 

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:

http://lists.xensource.com/archives/html/xen-devel/2010-10/msg00872.html 

Dan

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)

             reply	other threads:[~2011-06-09 21:55 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-06-09 21:55 Dan Magenheimer [this message]
2011-06-09 22:08 ` vsyscalls may be going away... impact on Xen time performance on Linux in the future? Jeremy Fitzhardinge
2011-06-09 22:39   ` Dan Magenheimer

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