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Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new comman
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero |
Date: |
Thu, 11 Apr 2013 17:45:34 +0300 |
On Thu, Apr 11, 2013 at 04:15:54PM +0200, Paolo Bonzini wrote:
> Il 11/04/2013 15:24, Michael R. Hines ha scritto:
> > That's very accurate. Zero page scanning *after* the bulk phase
> > is not very helpful in general.
> >
> > Are we proposing to skip is_dup_page() after the bulk phase
> > has finished?
>
> No, I'm saying that is_dup_page() should not be a problem. I'm saying
> it should only loop a lot during the bulk phase. The only effect I can
> imagine after the bulk phase is one cache miss.
>
> Perhaps the stress-test you're using does not reproduce realistic
> conditions with respect to zero pages. Peter Lieven benchmarked real
> guests, both Linux and Windows, and confirmed the theory that I
> mentioned upthread. Almost all non-zero pages are detected within the
> first few words, and almost all zero pages come from the bulk phase.
>
> Considering that one cache miss, RDMA is indeed different here. TCP
> would have this cache miss later anyway, RDMA does not. Let's say 300
> cycles/miss; at 2.5 GHz that is 300/2500 microseconds, i.e 0.12
> microseconds per page. This would say that we can run is_dup_page on 30
> GB worth of nonzero pages every second or more. Ok, the estimate is
> quite generous in many ways, but is_dup_page() is only a bottleneck if
> it can do less than 5 GB/s.
>
> Paolo
Further, if we read the pagemap to detect duplicates,
we won't need to read the page for RDMA either.
This might or might not prove to be a win, but
one thing for sure, management will not be able
to know if it's a win.
--
MST
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, (continued)
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Paolo Bonzini, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael S. Tsirkin, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael R. Hines, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael S. Tsirkin, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael R. Hines, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Paolo Bonzini, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael R. Hines, 2013/04/11
- Message not available
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael R. Hines, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael R. Hines, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Paolo Bonzini, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael R. Hines, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael S. Tsirkin, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Paolo Bonzini, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael R. Hines, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Paolo Bonzini, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael R. Hines, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Paolo Bonzini, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Eric Blake, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Michael R. Hines, 2013/04/11
- Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero, Eric Blake, 2013/04/11