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Subject: RE: Can we increase vring size over 1024?
> -----Original Message----- > From: Michael S. Tsirkin [mailto:email@example.com] > Sent: Saturday, September 03, 2016 1:33 AM > To: Gonglei (Arei) > Cc: firstname.lastname@example.org; email@example.com; firstname.lastname@example.org; > email@example.com; firstname.lastname@example.org; Lilijun (Jerry); > Huangpeng (Peter) > Subject: Re: Can we increase vring size over 1024? > > On Fri, Sep 02, 2016 at 06:55:35AM +0000, Gonglei (Arei) wrote: > > Hi Michael & all, > > > > Michael, you made a presentation about the virto 1.1's new features in KVM > Forum last week. > > That's wonderful! > > > > And I'd like to know can we increase vring size over 1024, such as 4096 or > 8192? > > > > My colleage had asked the same question in 2014, but she didn't get a > definite answare, > > So, I want to rewake up the dissusstion about this. Becase for the > virtio-crypto device, > > I also need to increase the vring size to get better performance and > thoughput, but the Qemu > > side limit the thought as VIRTQUEUE_MAX_SIZE is 1024. > > > > [QA-virtio]:Why vring size is limited to 1024? > > > http://qemu.11.n7.nabble.com/QA-virtio-Why-vring-size-is-limited-to-1024-td2 > 92450.html > > > > Avi Kivity said that google cloud exposed the vring size to 16k. > > > > Regards, > > -Gonglei > > Fundamentally, the reason is that the ring size > currently also sets the max s/g list length, and linux > hosts can't support bigger lists. > But I don't think this is a problem. Vring is just a container, we can say the max request's length is 1024, but the capacity of container shouldn't be the length of max request. For example, we can put 4K requests with one s/g list into vring at one time if the vring size is 4096, and 4 requests with 1024 s/g list into vring at one time. Ignoring the indirect table support. Am I right? > We should fix that in 1.1. > Sounds good! > -- > MST Regards, -Gonglei