Re: [PATCH v4 3/3] multifd: Implement zerocopy write in multifd migration (multifd-zerocopy)

[Leonardo Bras Soares Passos]

On Wed, Nov 3, 2021 at 8:24 PM Juan Quintela <quintela@redhat.com> wrote:
>
> Leonardo Bras Soares Passos <leobras@redhat.com> wrote:
> > Hello Juan,
>
> hi
>
> > Current multifd's sendmsg() will block until all data is sent, is that 
> > correct?
> >
> > If that's the case, and supposing the network driver supports
> > multiqueue, maybe there is a small chance for this to happen.
> > I will add the flush at the end of each iteration, just to be sure.
> >
> >>
> >> After each iteration, one needs to be sure that no ram is inflight.
> >>
> >> This means that I think you don't need the last_sync parameter at all,
> >> as you have to do the flush() in every iteration.
>
> It means guest memory corruption, it _needs_ to be there.
> That is the whole reason why multifd code has to wait after each
> iteration for all channels to finish.  Probability of failure is low,
> but it exist, so it needs to be handled correctly.

Sure, I will add a flush after each iteration.

> >> >              '*multifd-zlib-level': 'uint8',
> >> >              '*multifd-zstd-level': 'uint8',
> >> > +         '*multifd-zerocopy': 'bool',
> >> >              '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ] } }
> >>
> >> Something weird here.
> >>
> >> >              '*multifd-compression': 'MultiFDCompression',
> >> >              '*multifd-zlib-level': 'uint8',
> >> >              '*multifd-zstd-level': 'uint8',
> >> > +         '*multifd-zerocopy': 'bool',
> >> >              '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ] } }
> >> >
> >>
> >> Same here.
> >
> > Could you please elaborate?
>
> Indentation,
>
> +         '*multifd-zerocopy': 'bool',
>              '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ] } }
>
> This is how it is seen here.  space/tab?

It was supposed to be using only spaces.
I will make sure to fix that.

>
> Later, Juan.
>
Thanks!

Best regards,
Leo