> -----Original Message----- > From: rka...@virtuozzo.com [mailto:rka...@virtuozzo.com] > Sent: Wednesday, November 29, 2017 1:56 PM > To: Gonglei (Arei) > Cc: Eduardo Habkost; Denis V. Lunev; longpeng; Michael S. Tsirkin; Denis > Plotnikov; pbonz...@redhat.com; r...@twiddle.net; qemu-devel@nongnu.org; > huangpeng; Zhaoshenglong > Subject: Re: [Qemu-devel] [PATCH] i386: turn off l3-cache property by default > > On Wed, Nov 29, 2017 at 01:57:14AM +0000, Gonglei (Arei) wrote: > > > On Tue, Nov 28, 2017 at 11:20:27PM +0300, Denis V. Lunev wrote: > > > > On 11/28/2017 10:58 PM, Eduardo Habkost wrote: > > > > > On Fri, Nov 24, 2017 at 04:26:50PM +0300, Denis Plotnikov wrote: > > > > >> Commit 14c985cffa "target-i386: present virtual L3 cache info for > vcpus" > > > > >> introduced and set by default exposing l3 to the guest. > > > > >> > > > > >> The motivation behind it was that in the Linux scheduler, when waking > up > > > > >> a task on a sibling CPU, the task was put onto the target CPU's > runqueue > > > > >> directly, without sending a reschedule IPI. Reduction in the IPI > > > > >> count > > > > >> led to performance gain. > > > > >> > > > > Yes, that's one thing. > > > > The other reason for enabling L3 cache is the performance of accessing > memory. > > I guess you're talking about the super-smart buffer size tuning glibc > does in its memcpy and friends. We try to control that with an atomic > test for memcpy, and we didn't notice a difference. We'll need to > double-check... > > > We tested it by Stream benchmark, the performance is better with > L3-cache=on. > > This one: https://www.cs.virginia.edu/stream/ ? Thanks, we'll have a > look, too. > Yes. :)
Thanks, -Gonglei