From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH rdma-core 1/2] verbs: Report the device's PCI write end paddding capability Date: Tue, 14 Nov 2017 13:30:59 -0700 Message-ID: <20171114203059.GR4263@ziepe.ca> References: <1510667228-18579-1-git-send-email-yishaih@mellanox.com> <1510667228-18579-2-git-send-email-yishaih@mellanox.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1510667228-18579-2-git-send-email-yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Yishai Hadas Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, noaos-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, majd-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org List-Id: linux-rdma@vger.kernel.org On Tue, Nov 14, 2017 at 03:47:07PM +0200, Yishai Hadas wrote: > From: Noa Osherovich > > There are PCIe root complex that are able to optimize their > performance when incoming data is multiple full cache lines. > Expose the device capability to report whether the device supports > padding the ending of incoming packets to full cache line, such that > the last upstream write generated by the incoming packet will be a > full cache line. > > User should consider several factors before activating this feature: > - In case of high CPU memory load (which may cause PCI backpressure in > turn), if a large percent of the writes are partial cache line, this > feature should be checked as an optional solution. > - This feature might reduce performance if most packets are between > one and two cache lines and PCIe throughput has reached its maximum > capacity. E.g. 65B packet from the network port will lead to 128B > write on PCIe, which may cause trafiic on PCIe to reach high > throughput. This commit message would make a far better man page revision than what was provided :( Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html