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Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH t
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context |
Date: |
Fri, 13 Feb 2015 18:29:41 +0800 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Fri, 02/13 10:38, Paolo Bonzini wrote:
>
>
> On 13/02/2015 02:21, Fam Zheng wrote:
> >> Could you just do set_aio_context for all devices when starting
> >> dataplane? For example with a new scsi_device_set_aio_context function
> >> (and a new method in SCSIDeviceClass).
> >>
> >> Maybe I'm missing the obvious. :)
> >
> > Per VQ IOThread stills needs it, in the case that guest switches the VQ of a
> > disk on the fly.
>
> Per VQ iothread is far away though. Multiqueue aims at parallelizing
> accesses *to the same disk from different CPUs*, not at parallelizing
> accesses to different disks. As long as bdrv_set_aio_context does
> bdrv_drain_all, something has to change for multiqueue dataplane: either
> stop using bdrv_set_aio_context, or stop doing bdrv_drain_all.
>
> In either case, the changes are large enough that we shouldn't code for
> a case that doesn't exist yet.
>
> In addition, making the code more similar for virtio-blk and virtio-scsi
> dataplane is good, because the same changes can apply to both in the future.
I think we should avoid duplicate everything on both virtio-blk and
virtio-scsi, so they will have differences.
Why do you think Per VQ iothread is far away? Limiting to 1 thread for the
whole scsi bus doesn't sound ultimate solution for me. I think it's not harder
than the MMIO safety work we have, and also somehow independent to it.
But yes, stop using bdrv_set_aio_context will be the other way to make it
right, just harder to do.
Fam
- [Qemu-devel] [PATCH 0/3] virtio-scsi: Fix unsafe bdrv_set_aio_context calls, Fam Zheng, 2015/02/12
- [Qemu-devel] [PATCH 2/3] virtio-scsi: Deduplicate cmd queue handling code of dataplane, Fam Zheng, 2015/02/12
- [Qemu-devel] [PATCH 1/3] block: Forbid bdrv_set_aio_context outside BQL, Fam Zheng, 2015/02/12
- [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Fam Zheng, 2015/02/12
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Paolo Bonzini, 2015/02/12
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Fam Zheng, 2015/02/12
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Paolo Bonzini, 2015/02/13
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context,
Fam Zheng <=
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Paolo Bonzini, 2015/02/13
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Fam Zheng, 2015/02/13
- Re: [Qemu-devel] [PATCH 3/3] virtio-scsi-dataplane: Use main thread BH to set BDS' aio context, Paolo Bonzini, 2015/02/13