search for: vhost_max_pend

We used to stop the handling of tx when the number of pending DMAs exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation of both host and guest. But it was too aggressive in some cases, since any delay or blocking of a single packet may delay or block the guest transmission. Consider the following setup: +-----+ +-----+ | VM1 | | VM2 | +--+--+...

We used to stop the handling of tx when the number of pending DMAs exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation of both host and guest. But it was too aggressive in some cases, since any delay or blocking of a single packet may delay or block the guest transmission. Consider the following setup: +-----+ +-----+ | VM1 | | VM2 | +--+--+...

On 02/25/2014 09:57 PM, Michael S. Tsirkin wrote: > On Tue, Feb 25, 2014 at 02:53:58PM +0800, Jason Wang wrote: >> We used to stop the handling of tx when the number of pending DMAs >> exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation >> of both host and guest. But it was too aggressive in some cases, since >> any delay or blocking of a single packet may delay or block the guest >> transmission. Consider the following setup: >> >> +-----+ +--...

On 02/25/2014 09:57 PM, Michael S. Tsirkin wrote: > On Tue, Feb 25, 2014 at 02:53:58PM +0800, Jason Wang wrote: >> We used to stop the handling of tx when the number of pending DMAs >> exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation >> of both host and guest. But it was too aggressive in some cases, since >> any delay or blocking of a single packet may delay or block the guest >> transmission. Consider the following setup: >> >> +-----+ +--...

...Chuanyu wrote: > On 2014/2/26 13:53, Jason Wang wrote: >> On 02/25/2014 09:57 PM, Michael S. Tsirkin wrote: >>> On Tue, Feb 25, 2014 at 02:53:58PM +0800, Jason Wang wrote: >>>> We used to stop the handling of tx when the number of pending DMAs >>>> exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation >>>> of both host and guest. But it was too aggressive in some cases, since >>>> any delay or blocking of a single packet may delay or block the guest >>>> transmission. Consider the following setup: >>>>...

...Chuanyu wrote: > On 2014/2/26 13:53, Jason Wang wrote: >> On 02/25/2014 09:57 PM, Michael S. Tsirkin wrote: >>> On Tue, Feb 25, 2014 at 02:53:58PM +0800, Jason Wang wrote: >>>> We used to stop the handling of tx when the number of pending DMAs >>>> exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation >>>> of both host and guest. But it was too aggressive in some cases, since >>>> any delay or blocking of a single packet may delay or block the guest >>>> transmission. Consider the following setup: >>>>...

...9:57 PM, Michael S. Tsirkin wrote: >>>>> > >>>On Tue, Feb 25, 2014 at 02:53:58PM +0800, Jason Wang wrote: >>>>>> > >>>>We used to stop the handling of tx when the number of pending DMAs >>>>>> > >>>>exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation >>>>>> > >>>>of both host and guest. But it was too aggressive in some cases, since >>>>>> > >>>>any delay or blocking of a single packet may delay or block the guest >>>>>...

...9:57 PM, Michael S. Tsirkin wrote: >>>>> > >>>On Tue, Feb 25, 2014 at 02:53:58PM +0800, Jason Wang wrote: >>>>>> > >>>>We used to stop the handling of tx when the number of pending DMAs >>>>>> > >>>>exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation >>>>>> > >>>>of both host and guest. But it was too aggressive in some cases, since >>>>>> > >>>>any delay or blocking of a single packet may delay or block the guest >>>>>...

On 2014/2/26 13:53, Jason Wang wrote: > On 02/25/2014 09:57 PM, Michael S. Tsirkin wrote: >> On Tue, Feb 25, 2014 at 02:53:58PM +0800, Jason Wang wrote: >>> We used to stop the handling of tx when the number of pending DMAs >>> exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation >>> of both host and guest. But it was too aggressive in some cases, since >>> any delay or blocking of a single packet may delay or block the guest >>> transmission. Consider the following setup: >>> >>>...

We used to stop the handling of tx when the number of pending DMAs exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation of both host and guest. But it was too aggressive in some cases, since any delay or blocking of a single packet may delay or block the guest transmission. Consider the following setup: +-----+ +-----+ | VM1 | | VM2 | +--+--+...

We used to stop the handling of tx when the number of pending DMAs exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation of both host and guest. But it was too aggressive in some cases, since any delay or blocking of a single packet may delay or block the guest transmission. Consider the following setup: +-----+ +-----+ | VM1 | | VM2 | +--+--+...

On Tue, Feb 25, 2014 at 02:53:58PM +0800, Jason Wang wrote: > We used to stop the handling of tx when the number of pending DMAs > exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation > of both host and guest. But it was too aggressive in some cases, since > any delay or blocking of a single packet may delay or block the guest > transmission. Consider the following setup: > > +-----+ +-----+ > | VM1...

...er this patch, the large flow is still rate limited, while the small reverts to its original rate. See also discussion in the first link, below. The limit in vhost_exceeds_maxpend must be carefully chosen. When vq->num >> 1, the flows remain correlated. This value happens to correspond to VHOST_MAX_PENDING for vq->num == 256. Allow smaller fractions and ensure correctness also for much smaller values of vq->num, by testing the min() of both explicitly. See also the discussion in the second link below. Link:http://lkml.kernel.org/r/CAF=yD-+Wk9sc9dXMUq1+x_hh=3ThTXa6BnZkygP3tgVpjbp93g at mail....

...er this patch, the large flow is still rate limited, while the small reverts to its original rate. See also discussion in the first link, below. The limit in vhost_exceeds_maxpend must be carefully chosen. When vq->num >> 1, the flows remain correlated. This value happens to correspond to VHOST_MAX_PENDING for vq->num == 256. Allow smaller fractions and ensure correctness also for much smaller values of vq->num, by testing the min() of both explicitly. See also the discussion in the second link below. Link:http://lkml.kernel.org/r/CAF=yD-+Wk9sc9dXMUq1+x_hh=3ThTXa6BnZkygP3tgVpjbp93g at mail....

...ding packets. > > So this patch moves the check into main loop. Tests shows about 5%-10% > improvement on per cpu throughput for guest tx. But a 5% drop on per cpu > transaction rate for a single session TCP_RR. Any explanation for the drop? single session TCP_RR is unlikely to exceed VHOST_MAX_PEND, correct? > > Signed-off-by: Jason Wang <jasowang at redhat.com> > --- > drivers/vhost/net.c | 15 ++++----------- > 1 files changed, 4 insertions(+), 11 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index d09c17c..592e1f2 100644 >...

...ding packets. > > So this patch moves the check into main loop. Tests shows about 5%-10% > improvement on per cpu throughput for guest tx. But a 5% drop on per cpu > transaction rate for a single session TCP_RR. Any explanation for the drop? single session TCP_RR is unlikely to exceed VHOST_MAX_PEND, correct? > > Signed-off-by: Jason Wang <jasowang at redhat.com> > --- > drivers/vhost/net.c | 15 ++++----------- > 1 files changed, 4 insertions(+), 11 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index d09c17c..592e1f2 100644 >...

...>On 2014/2/26 13:53, Jason Wang wrote: > >>On 02/25/2014 09:57 PM, Michael S. Tsirkin wrote: > >>>On Tue, Feb 25, 2014 at 02:53:58PM +0800, Jason Wang wrote: > >>>>We used to stop the handling of tx when the number of pending DMAs > >>>>exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation > >>>>of both host and guest. But it was too aggressive in some cases, since > >>>>any delay or blocking of a single packet may delay or block the guest > >>>>transmission. Consider the following setup: >...

On 08/20/2013 10:48 AM, Jason Wang wrote: > On 08/16/2013 06:02 PM, Michael S. Tsirkin wrote: >> > On Fri, Aug 16, 2013 at 01:16:30PM +0800, Jason Wang wrote: >>> >> We used to limit the max pending DMAs to prevent guest from pinning too many >>> >> pages. But this could be removed since: >>> >> >>> >> - We have the

On 08/20/2013 10:48 AM, Jason Wang wrote: > On 08/16/2013 06:02 PM, Michael S. Tsirkin wrote: >> > On Fri, Aug 16, 2013 at 01:16:30PM +0800, Jason Wang wrote: >>> >> We used to limit the max pending DMAs to prevent guest from pinning too many >>> >> pages. But this could be removed since: >>> >> >>> >> - We have the

On Fri, Mar 07, 2014 at 01:28:27PM +0800, Jason Wang wrote: > We used to stop the handling of tx when the number of pending DMAs > exceeds VHOST_MAX_PEND. This is used to reduce the memory occupation > of both host and guest. But it was too aggressive in some cases, since > any delay or blocking of a single packet may delay or block the guest > transmission. Consider the following setup: > > +-----+ +-----+ > | VM1...