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From: | malc |
Subject: | [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2 |
Date: | Tue, 21 Aug 2007 23:44:57 +0400 (MSD) |
On Tue, 21 Aug 2007, Luca Tettamanti wrote:
Avi Kivity ha scritto:Luca Tettamanti wrote:At 1000Hz: QEMU hpet 5.5% dynticks 11.7% KVM hpet 3.4% dynticks 7.3% No surprises here, you can see the additional 1k syscalls per second.This is very surprising to me. The 6.2% difference for the qemu case translates to 62ms per second, or 62us per tick at 1000Hz. That's more than a hundred simple syscalls on modern processors. We shouldn't have to issue a hundred syscalls per guest clock tick.
[..snip preulde..]
I've also tried APC which was suggested by malc[1] and: - readings are far more stable - the gap between dynticks and non-dynticks seems not significant
[..dont snip the obvious fact and snip the numbers..]
Luca [1] copy_to_user inside spinlock is a big no-no ;)
[..notice a projectile targeting at you and rush to see the code..] Mixed feelings about this... But in principle the code ofcourse is dangerous, thank you kindly for pointing this out. I see two ways out of this: a. moving the lock/unlock inside the loop with unlock preceding sometimes sleep deprived copy_to_user b. fill temporaries and after the loop is done copy it in one go Too late, too hot, i wouldn't mind beying on a receiving side of a good advice. -- vale
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