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Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates |
Date: |
Thu, 30 Nov 2017 13:58:20 +0100 |
On Thu, 30 Nov 2017 12:47:20 +0000
"Dr. David Alan Gilbert" <address@hidden> wrote:
> * Igor Mammedov (address@hidden) wrote:
> > On Thu, 30 Nov 2017 12:08:06 +0000
> > "Dr. David Alan Gilbert" <address@hidden> wrote:
> >
> > > * Igor Mammedov (address@hidden) wrote:
> > > > On Wed, 29 Nov 2017 18:50:19 +0000
> > > > "Dr. David Alan Gilbert (git)" <address@hidden> wrote:
> > > >
> > > > > From: "Dr. David Alan Gilbert" <address@hidden>
> > > > >
> > > > > Hi,
> > > > > This is an experimental set that reworks the way the vhost
> > > > > code handles changes in physical address space layout that
> > > > > came from a discussion with Igor.
> > > > Thanks for looking into it.
> > > >
> > > >
> > > > > Instead of updating and trying to merge sections of address
> > > > > space on each add/remove callback, we wait until the commit phase
> > > > > and go through and rebuild a list by walking the Flatview of
> > > > > memory and end up producing an ordered list.
> > > > > We compare the list to the old list to trigger updates.
> > > > >
> > > > > Note, only very lightly tested so far, I'm just trying to see if it's
> > > > > the right shape.
> > > > >
> > > > > Igor, is this what you were intending?
> > > >
> > > > I was thinking about a little less intrusive approach
> > > >
> > > > where vhost_region_add/del are modified to maintain
> > > > sorted by GPA array of mem_sections, vhost_dev::mem is dropped
> > > > altogether and vhost_memory_region array is build/used/freed
> > > > on every vhost_commit().
> > > > Maintaining sorted array should roughly cost us O(2 log n) if
> > > > binary search is used.
> > > >
> > > > However I like your idea with iterator even more as it have
> > > > potential to make it even faster O(n) if we get rid of
> > > > quadratic and relatively complex vhost_update_compare_list().
> > >
> > > Note vhost_update_compare_list is complex,
> > > but it is O(n) - it's
> > > got nested loops, but the inner loop moves forward and oldi never
> > > gets reset back to zero.
> > While skimming through patches I've overlooked it.
> >
> > Anyways,
> > why memcmp(old_arr, new_arr) is not sufficient
> > to detect a change in memory map?
>
> It tells you that you've got a change, but doesn't give
> the start/end of the range that's changed, and those
> are used by vhost_commit to limit the work of
> vhost_verify_ring_mappings.
Isn't memmap list a sorted and
dev->mem_changed_[start|end]_addr are the lowest|highest
addresses of whole map?
If it's, so wouldn't getting values directly from
the 1st/last entries of array be sufficient?
>
> Dave
>
> > >
> > > > Pls, see comments on individual patches.
> > >
> > > Thanks; I have fixed a couple of bugs since I posted, so I'm
> > > more interested in structure/shape. Any good ideas how to test
> > > it are welcome.
> > >
> > > Dave
> > >
> > > >
> > > > > Dave
> > > > >
> > > > > Dr. David Alan Gilbert (7):
> > > > > memory: address_space_iterate
> > > > > vhost: Move log_dirty check
> > > > > vhost: New memory update functions
> > > > > vhost: update_mem_cb implementation
> > > > > vhost: Compare new and old memory lists
> > > > > vhost: Copy updated region data into device state
> > > > > vhost: Remove vhost_set_memory and children
> > > > >
> > > > > hw/virtio/trace-events | 8 +
> > > > > hw/virtio/vhost.c | 424
> > > > > ++++++++++++++++++++++---------------------------
> > > > > include/exec/memory.h | 23 +++
> > > > > memory.c | 22 +++
> > > > > 4 files changed, 241 insertions(+), 236 deletions(-)
> > > > >
> > > >
> > > --
> > > Dr. David Alan Gilbert / address@hidden / Manchester, UK
> >
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [RFC 3/7] vhost: New memory update functions, (continued)
- [Qemu-devel] [RFC 5/7] vhost: Compare new and old memory lists, Dr. David Alan Gilbert (git), 2017/11/29
- [Qemu-devel] [RFC 4/7] vhost: update_mem_cb implementation, Dr. David Alan Gilbert (git), 2017/11/29
- [Qemu-devel] [RFC 7/7] vhost: Remove vhost_set_memory and children, Dr. David Alan Gilbert (git), 2017/11/29
- [Qemu-devel] [RFC 6/7] vhost: Copy updated region data into device state, Dr. David Alan Gilbert (git), 2017/11/29
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates, Igor Mammedov, 2017/11/30
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates, Dr. David Alan Gilbert, 2017/11/30
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates, Igor Mammedov, 2017/11/30
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates, Dr. David Alan Gilbert, 2017/11/30
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates,
Igor Mammedov <=
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates, Dr. David Alan Gilbert, 2017/11/30
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates, Igor Mammedov, 2017/11/30
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates, Dr. David Alan Gilbert, 2017/11/30
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates, Igor Mammedov, 2017/11/30
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates, Dr. David Alan Gilbert, 2017/11/30
- Re: [Qemu-devel] [RFC 0/7] Rework vhost memory region updates, Greg Kurz, 2017/11/30