On Thu, 3 Oct 2019 18:57:32 +0200 Ilya Maximets <i.maxim...@ovn.org> wrote:
> On 02.10.2019 20:15, Flavio Leitner wrote: > > On Wed, 2 Oct 2019 17:50:41 +0000 > > Shahaf Shuler <shah...@mellanox.com> wrote: > > > >> Wednesday, October 2, 2019 3:59 PM, Flavio Leitner: > >>> Obrembski MichalX <michalx.obremb...@intel.com>; Stokes Ian > >>> <ian.sto...@intel.com> > >>> Subject: Re: [dpdk-dev] [PATCH] vhost: add support to large linear > >>> mbufs > >>> > >>> > >>> Hi Shahaf, > >>> > >>> Thanks for looking into this, see my inline comments. > >>> > >>> On Wed, 2 Oct 2019 09:00:11 +0000 > >>> Shahaf Shuler <shah...@mellanox.com> wrote: > >>> > >>>> Wednesday, October 2, 2019 11:05 AM, David Marchand: > >>>>> Subject: Re: [dpdk-dev] [PATCH] vhost: add support to large > >>>>> linear mbufs > >>>>> > >>>>> Hello Shahaf, > >>>>> > >>>>> On Wed, Oct 2, 2019 at 6:46 AM Shahaf Shuler > >>>>> <shah...@mellanox.com> wrote: > >>>>>> > >> > >> [...] > >> > >>>>> > >>>>> I am missing some piece here. > >>>>> Which pool would the PMD take those external buffers from? > >>>> > >>>> The mbuf is always taken from the single mempool associated w/ > >>>> the rxq. The buffer for the mbuf may be allocated (in case virtio > >>>> payload is bigger than current mbuf size) from DPDK hugepages or > >>>> any other system memory and be attached to the mbuf. > >>>> > >>>> You can see example implementation of it in mlx5 PMD (checkout > >>>> rte_pktmbuf_attach_extbuf call) > >>> > >>> Thanks, I wasn't aware of external buffers. > >>> > >>> I see that attaching external buffers of the correct size would be > >>> more efficient in terms of saving memory/avoiding sparsing. > >>> > >>> However, we still need to be prepared to the worse case scenario > >>> (all packets 64K), so that doesn't help with the total memory > >>> required. > >> > >> Am not sure why. > >> The allocation can be per demand. That is - only when you > >> encounter a large buffer. > >> > >> Having buffer allocated in advance will benefit only from removing > >> the cost of the rte_*malloc. However on such big buffers, and > >> further more w/ device offloads like TSO, am not sure that is an > >> issue. > > > > Now I see what you're saying. I was thinking we had to reserve the > > memory before, like mempool does, then get the buffers as needed. > > > > OK, I can give a try with rte_*malloc and see how it goes. > > This way we actually could have a nice API. For example, by > introducing some new flag RTE_VHOST_USER_NO_CHAINED_MBUFS (there > might be better name) which could be passed to driver_register(). > On receive, depending on this flag, function will create chained > mbufs or allocate new contiguous memory chunk and attach it as > an external buffer if the data could not be stored in a single > mbuf from the registered memory pool. > > Supporting external memory in mbufs will require some additional > work from the OVS side (e.g. better work with ol_flags), but > we'll have to do it anyway for upgrade to DPDK 19.11. Agreed. Looks like rte_malloc is fast enough after all. I have a PoC running iperf3 from VM to another baremetal using vhost-user client with TSO enabled: [...] [ 5] 140.00-141.00 sec 4.60 GBytes 39.5 Gbits/sec 0 1.26 MBytes [ 5] 141.00-142.00 sec 4.65 GBytes 39.9 Gbits/sec 0 1.26 MBytes [ 5] 142.00-143.00 sec 4.65 GBytes 40.0 Gbits/sec 0 1.26 MBytes [ 5] 143.00-144.00 sec 4.65 GBytes 39.9 Gbits/sec 9 1.04 MBytes [ 5] 144.00-145.00 sec 4.59 GBytes 39.4 Gbits/sec 0 1.16 MBytes [ 5] 145.00-146.00 sec 4.58 GBytes 39.3 Gbits/sec 0 1.26 MBytes [ 5] 146.00-147.00 sec 4.48 GBytes 38.5 Gbits/sec 700 973 KBytes [...] (The physical link is 40Gbps) I will clean that, test more and post the patches soon. Thanks! fbl
