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Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading prepa
From: |
Liu Bo |
Subject: |
Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3 |
Date: |
Sat, 10 Aug 2019 14:34:00 -0700 |
User-agent: |
NeoMutt/20180323 |
On Fri, Aug 09, 2019 at 09:21:02AM +0100, Stefan Hajnoczi wrote:
> On Thu, Aug 08, 2019 at 10:53:16AM +0100, Dr. David Alan Gilbert wrote:
> > * Stefan Hajnoczi (address@hidden) wrote:
> > > On Wed, Aug 07, 2019 at 04:57:15PM -0400, Vivek Goyal wrote:
> > > 2. Can MAP/UNMAP be performed directly in QEMU via a separate virtqueue?
> >
> > I think there's two things to solve here that I don't currently know the
> > answer to:
> > 2a) We'd need to get the fd to qemu for the thing to mmap;
> > we might be able to cache the fd on the qemu side for existing
> > mappings, so when asking for a new mapping for an existing file then
> > it would already have the fd.
> >
> > 2b) Running a device with a mix of queues inside QEMU and on
> > vhost-user; I don't think we have anything with that mix
>
> vhost-user-net works in the same way. The ctrl queue is handled by QEMU
> and the rx/tx queues by the vhost device. This is in fact how vhost was
> initially designed: the vhost device is not a full virtio device, only
> the dataplane.
> > > 3. Can READ/WRITE be performed directly in QEMU via a separate virtqueue
> > > to eliminate the bad address problem?
> >
> > Are you thinking of doing all read/writes that way, or just the corner
> > cases? It doesn't seem worth it for the corner cases unless you're
> > finding them cropping up in real work loads.
>
> Send all READ/WRITE requests to QEMU instead of virtiofsd.
>
> Only handle metadata requests in virtiofsd (OPEN, RELEASE, READDIR,
> MKDIR, etc).
For now qemu is not aware of virtio-fs's fd info, but I think it's
doable, I like the idea.
thanks,
-liubo
>
> > > I'm not going to tackle DAX optimization myself right now but wanted to
> > > share these ideas.
> >
> > One I was thinking about that feels easier than (2) was to change the
> > vhost slave protocol to be split transaction; it wouldn't do anything
> > for the latency but it would be able to do some in parallel if we can
> > get the kernel to feed it.
>
> There are two cases:
> 1. mmapping multiple inode. This should benefit from parallelism,
> although mmap is still expensive because it involves TLB shootdown
> for all other threads running this process.
> 2. mmapping the same inode. Here the host kernel is likely to serialize
> mmaps even more, making it hard to gain performance.
>
> It's probably worth writing a tiny benchmark first to evaluate the
> potential gains.
>
> Stefan
> _______________________________________________
> Virtio-fs mailing list
> address@hidden
> https://www.redhat.com/mailman/listinfo/virtio-fs
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, (continued)
- Re: [Qemu-devel] [PATCH 0/4] virtiofsd: multithreading preparation part 3, Stefan Hajnoczi, 2019/08/07
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, Vivek Goyal, 2019/08/07
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, Stefan Hajnoczi, 2019/08/08
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, Dr. David Alan Gilbert, 2019/08/08
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, Vivek Goyal, 2019/08/08
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, Stefan Hajnoczi, 2019/08/09
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, Liu Bo, 2019/08/10
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, Stefan Hajnoczi, 2019/08/09
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3,
Liu Bo <=
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, piaojun, 2019/08/10
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, Stefan Hajnoczi, 2019/08/12
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, piaojun, 2019/08/12
- Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, Dr. David Alan Gilbert, 2019/08/12
Re: [Qemu-devel] [Virtio-fs] [PATCH 0/4] virtiofsd: multithreading preparation part 3, piaojun, 2019/08/08