Hi All, On the "“RSS hash threshold method” for EMC load shedding I hope to have time to do an RFC to illustrate in the next week or so give a better idea of what I mean.
Thanks, Billy. > -----Original Message----- > From: [email protected] [mailto:ovs-dev- > [email protected]] On Behalf Of Darrell Ball > Sent: Thursday, August 17, 2017 7:46 PM > To: Jan Scheurich <[email protected]>; Darrell Ball > <[email protected]> > Cc: [email protected] > Subject: Re: [ovs-dev] [PATCH v3 1/4] dpif-netdev: Skip EMC lookup/insert > for recirc packets > > > > On 8/17/17, 5:22 AM, "Jan Scheurich" <[email protected]> wrote: > > The RSS hash threshold method looks like the only pseudo-random > criterion that we can use that produces consistent result for every packet of > a flow and does require more information. Of course elephant flows with an > unlucky hash value might never get to use the EMC, but that risk we have > with any stateless selection scheme. > > > > [Darrell] It is probably something I know by another name, but JTBC, can > you define the “RSS hash threshold method” ? > > > > I am referring to Billy's proposal > (https://urldefense.proofpoint.com/v2/url?u=https- > 3A__mail.openvswitch.org_pipermail_ovs-2Ddev_2017- > 2DAugust_336509.html&d=DwIGaQ&c=Sqcl0Ez6M0X8aeM67LKIiDJAXVeAw- > YihVMNtXt- > uEs&r=dGZmbKhBG9tJHY4odedsGA&m=_i_IqWudJqU7R3_ZaFm7HHhOQM > Hwm_U6G- > EIyOGjkxI&s=IDMHVf9n5CjmHMI67mzMd0HZegNJ_LntZLfcdpRUvJI&e= ) > > > In essence the is suggests to only select packets for EMC lookup whose RSS > hash is above a certain threshold. The lookup probability is determined by > the threshold (e.g. threshold of 0.75 * UINT32_MAX corresponds to 25%). It > is pseudo-random as, assuming that the hash result is uniformly distributed, > flows will profit from EMC lookup with the same probability. > > > [Darrell] ahh, there is no actual patch yet, just an e-mail > I see, you have a coined the term “RSS hash threshold method” > for > the approach; the nomenclature makes sense now. > I’ll have separate comments, of course, on the proposal > itself. > > > > The new thing required will be the dynamic adjustment of lookup > probability to the EMC fill level and/or hit ratio. > > > > [Darrell] Did you mean insertion probability rather than lookup > probability ? > > > > No, I actually meant dynamic adaptation of lookup probability. We don't > want to reduce the EMC lookup probability when the EMC is not yet > overloaded, but only when the EMC hit rate degrades due to collisions. > When we devise an algorithm to adapt lookup probability, we can study if it > could make sense to also dynamically adjust the currently fixed > (configurable) EMC insertion probability based on EMC fill level and/or hit > rate. > > > [Darrell] Now that I know what you are referring to above, it is a lot easier > to > make the linkage. > > > > BR, Jan > > > > _______________________________________________ > dev mailing list > [email protected] > https://mail.openvswitch.org/mailman/listinfo/ovs-dev _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
