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Message-ID: <87pq1c1uj4.fsf@rustcorp.com.au> Date: Fri, 11 Jan 2013 10:05:11 +1030 From: Rusty Russell <rusty@...tcorp.com.au> To: Sjur Brændeland <sjurbren@...il.com> Cc: "Michael S. Tsirkin" <mst@...hat.com>, Linus Walleij <linus.walleij@...aro.org>, virtualization@...ts.linux-foundation.org, LKML <linux-kernel@...r.kernel.org>, Sjur Brændeland <sjur.brandeland@...ricsson.com>, Ohad Ben-Cohen <ohad@...ery.com> Subject: Re: [RFCv2 00/12] Introduce host-side virtio queue and CAIF Virtio. Sjur Brændeland <sjurbren@...il.com> writes: > Hi Rusty, > > On Thu, Jan 10, 2013 at 11:30 AM, Rusty Russell <rusty@...tcorp.com.au> wrote: > ... >>I now have some lightly-tested code (via a userspace harness). > > Great - thank you for looking into this. I will start integrating this > with my patches > when you send out a proper patch. Hi Sjur! OK, the Internet was no help here, how do you pronounce Sjur? I'm guessing "shoor" rhyming with tour until I know better. >> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig >> index 8d5bddb..fd95d3e 100644 >> --- a/drivers/virtio/Kconfig >> +++ b/drivers/virtio/Kconfig >> @@ -5,6 +5,12 @@ config VIRTIO >> bus, such as CONFIG_VIRTIO_PCI, CONFIG_VIRTIO_MMIO, CONFIG_LGUEST, >> CONFIG_RPMSG or CONFIG_S390_GUEST. >> >> +config VHOST >> + tristate > > Inclusion of drivers/virtio from drivers/Makefile depends on VIRTIO. > So I guess VHOST should select VIRTIO to ensure that > drivers/virtio/virtio_host.c > is part of the build. Maybe I should move drivers/virtio/virtio_host.c to drivers/vhost/vringh.c; I'll look at it. It makes sense for vhost/ to contain the host-side stuff, since it already exists. >> + if (*last_avail_idx == avail_idx) >> + return vrh->vring.num; >> + >> + /* Only get avail ring entries after they have been exposed by guest. */ >> + smp_rmb(); > > We are accessing memory shared with a remote device (modem), so we probably > need mandatory barriers here, e.g. something like the virtio_rmb > defined in virtio_ring.c. Fair enough, we can put those in a header. >> + /* Append the pages into the sg. */ >> + err = add_to_sg(&vsg, (void *)(long)acc->desc.addr, >> + acc->desc.len, gfp); > > I would prefer not to split into pages at this point, but rather provide an > iterator or the original list found in the descriptor to the client. > > In our case we use virtio rings to talk to a LTE-modem over shared memory. > The IP traffic is received over the air, interleaved and arrives in > the virtio driver in > large bursts. So virtio driver on the modem receives multiple datagrams > held in large contiguous buffers. Our current approach is to handle each > buffer as a chained descriptor list, where each datagram is kept in > separate chained descriptors. When the buffers are consumed on the linux > host, the modem will read the chained descriptors from the used-ring and > free the entire contiguous buffer in one operation. In other words, boundaries matter? While the sg-in-place hack is close to optimal for TCM_VHOST, neither net not you can use it directly. I'll switch to an iovec (with a similar use-caller-supplied-if-it-fits trick); they're smaller anyway. More code coming... Thanks, Rusty. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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