|
From: | Avi Kivity |
Subject: | [Qemu-devel] Re: [RFC] Moving the kvm ioapic, pic, and pit back to userspace |
Date: | Mon, 07 Jun 2010 22:16:55 +0300 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-3.fc13 Thunderbird/3.0.4 |
On 06/07/2010 09:54 PM, David S. Ahern wrote:
So it's important to know how often your RHEL3/4 guest queries the PIT (not just receives interrupts, actually reads the counter) under a realistic load. If you have such a number (in reads/sec) that would be a good input to this discussion.Aps that invoke gettimeofday a lot.
Ask a stupid question, get an "it depends on the workload" answer.
As I recall RHEL3 uses the TSC between timer interrupts, but RHEL4 samples counters on each gettimeofday call: http://www.mail-archive.com/address@hidden/msg07231.html Because of that performance of applications that timestamp log entries (like a certain product I work on) takes a hit on KVM unless the TSC is the clock source.
So it looks like dropping the PIT out of the kernel, let alone the PIC/IOAPIC, is out of the question.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
[Prev in Thread] | Current Thread | [Next in Thread] |