On Tue, 2008-03-04 at 18:50 -0600, Anthony Liguori wrote: > Dor Laor wrote: > > On Tue, 2008-03-04 at 09:52 -0600, Anthony Liguori wrote: > > > >> Yang, Sheng wrote: > >> > >>> Hi > >>> > >>> Here is the last in-kernel PIT patch for KVM. The mainly change from last > >>> version is the supporting to save/restore. I also tested live migration. > >>> > >>> The other modifies including some date structure changed to be better for > >>> supporting the save/restore. I moved the PIT timer to outside of channel > >>> structure, which explicitly means only one channel (channel 0) would > >>> trigger > >>> it. > >>> > >>> After fix TSC problem on SMP PAE RHEL5/5.1 guest, now the patch works > >>> well > >>> without any modify of kernel parameter. > >>> > >>> > >> How are you measuring the improvements from an in-kernel PIT? From your > >> mails, you're claiming it increases the timer accuracy. How are you > >> measuring it and how much does it improve it? > >> > >> > > > > It's also a functionality addition: userspace pit & pic combination > > needed to use -tdf option (time drift fix). The tdf took care of pending > > pit irqs and tried to make the guest ack the right number of irqs the > > pit was configured. > > > > I thought there was some discussion about whether -tdf was every useful > in practice?
It works. Just try to play a movie in windows standard HAL with and w/o -tdf --no-irq-chip and you'll see the difference. > > > Once we switched to the default in-kernel pic, the userspace pit > > couldn't get the acks from the pit. > > One can see the effect when running multiple guests (windows, standard > > HAL) playing video, the time slows down. > > > > Okay, that makes sense. So have you done any tests to confirm this? We > suffered through a fair number of regressions when we moved to an > in-kernel APIC. Before moving another big chunk of code in the kernel > and going through possible regressions, I want to make sure we have a > measurable argument that it's the right thing to do. > > So how do we measure the benefits of an in-kernel PIT? Play the same movie using the kernel's pit. > > Regards, > > Anthony Liguori > > > This patch set has a pending counter and takes care for it too. > > > > > >> Do you expect an overall performance improvement from this or is it > >> simply about improving timer accuracy? > >> > >> > > > > It will probably help older kernels with slow HZ run faster HZ guests. > > Without CONFIG_DYNTICK the guests behaved jumpy because of that. > > > > > >> Regards, > >> > >> Anthony Liguori > >> > >> > >> > >> ------------------------------------------------------------------------- > >> This SF.net email is sponsored by: Microsoft > >> Defy all challenges. Microsoft(R) Visual Studio 2008. > >> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > >> _______________________________________________ > >> kvm-devel mailing list > >> kvm-devel@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/kvm-devel > >> > > > > > ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
