Re: [External] Re: [PATCH] memory: avoid updating ioeventfds for some address_space

[Peter Xu <peterx@redhat.com>]

On Thu, Jul 27, 2023 at 09:23:34PM +0800, hongmainquan wrote:
> 
> 
> 在 2023/7/27 8:53 下午, Peter Xu 写道:
> > On Thu, Jul 27, 2023 at 11:59:43AM +0800, hongmainquan wrote:
> > > 
> > > 
> > > 在 2023/7/27 1:45 上午, Peter Xu 写道:
> > > > On Tue, Jul 25, 2023 at 07:20:37PM +0800, hongmianquan wrote:
> > > > > When updating ioeventfds, we need to iterate all address spaces,
> > > > > but some address spaces do not register eventfd_add|del call when
> > > > > memory_listener_register() and they do nothing when updating ioeventfds.
> > > > > So we can skip these AS in address_space_update_ioeventfds().
> > > > > 
> > > > > The overhead of memory_region_transaction_commit() can be significantly
> > > > > reduced. For example, a VM with 8 vhost net devices and each one has
> > > > > 64 vectors, can reduce the time spent on memory_region_transaction_commit by 20%.
> > > > > 
> > > > > Signed-off-by: hongmianquan <hongmianquan@bytedance.com>
> > > > 
> > > > Reviewed-by: Peter Xu <peterx@redhat.com>
> > > > 
> > > > Should be for 8.2, though.  Please always copy Paolo for memory related
> > > > patches.  I hope Paolo can see this.
> > > > 
> > > Thanks, I hope so. Also, I'm not quite sure what 'Should be for 8.2' means.
> > > Does it imply that there will be changes to this logic after version 8.2?
> > 
> > See:
> > 
> > https://wiki.qemu.org/Planning/8.1
> > 
> > We're already right before 8.1-rc2 release, perf patch isn't normally the
> > target of this phase.
> > 
> > Thanks,
> > 
> Understood. Hope for some suggestions from you.

No further suggestion from my side. You can just keep an eye on this patch
after the 8.1 release - it probably just won't get merged before that.

Some maintainers prefer a resend after the release, but many don't.  It's
optional in this case I think.

Thanks,

-- 
Peter Xu