From: David Gibson <david@gibson.dropbear.id.au>
To: qemu-devel@nongnu.org
Subject: [Qemu-devel] Avoiding nographic_timer exits
Date: Fri, 30 Sep 2011 18:18:49 +1000 [thread overview]
Message-ID: <20110930081849.GC4512@yookeroo.fritz.box> (raw)
With PowerKVM, exits from KVM to qemu are even more expensive than on
x86. One significant source of these we're finding (since we usually
work in -nographic mode) is the nographic_timer.
At present, we're using a hack to disable it, but that's obviously not
a long term solution. From examination, it looks like the only
purpose of this timer is to flush coalesced mmios. So it seems like
the timer should only be activated when a coalesced mmio region
actually exists, but I'm not entirely sure how to go about that.
Thinking longer term, it seems very odd that a userspace periodic
timer handles this at all. Surely it would make more sense to use a
kernel timer within KVM, which can be activated only when there are
actually pending coalesced MMIOs in the buffer.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
next reply other threads:[~2011-09-30 8:38 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-30 8:18 David Gibson [this message]
2011-09-30 8:46 ` [Qemu-devel] Avoiding nographic_timer exits Jan Kiszka
2011-09-30 8:55 ` Jan Kiszka
2011-09-30 9:18 ` Jan Kiszka
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