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Date: Sun, 28 Sep 2014 13:49:21 -0700 From: Alexei Starovoitov <ast@...mgrid.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Or Gerlitz <gerlitz.or@...il.com>, "David S. Miller" <davem@...emloft.net>, Jesper Dangaard Brouer <brouer@...hat.com>, Eric Dumazet <edumazet@...gle.com>, John Fastabend <john.r.fastabend@...el.com>, Linux Netdev List <netdev@...r.kernel.org>, Amir Vadai <amirv@...lanox.com>, Or Gerlitz <or.gerlitz@...il.com> Subject: Re: [PATCH net-next] mlx4: optimize xmit path On Sun, Sep 28, 2014 at 11:52 AM, Eric Dumazet <eric.dumazet@...il.com> wrote: > On Sun, 2014-09-28 at 11:07 -0700, Alexei Starovoitov wrote: > >> this is great improvement! >> Thank you for leading this effort. >> 10G line rate is definitely nice :) >> Hopefully Or can demo similar numbers with 40G nic as well :) >> >> > + if (ring->bf_enabled && desc_size <= MAX_BF && !bounce && >> > + !vlan_tx_tag_present(skb) && send_doorbell) { >> >> feels something wrong here, since it checks for >> send_doorbell, but iowrite() happens in the 'else' part >> of this branch with another 'if (send_doorbell)' >> > > If we do not plan to send a doorbell, we should not use blueframe. > > Blueframe is always sending a doorbell by design, as it uses a single > flip buffer. > > So if you want to see any improvement thanks to skb->xmit_more, we have > to use the iowrite32(), not the blueframe. > > Therefore , if send_doorbell == false, we do not want the doorbell I see. So xmit_more=true overrides blueflame=on settings. I wonder what is the performance difference bf=on vs bf=off, also whether a burst of N packets via bf is slower than burst via queue+doorbell. Some fun exploration for driver experts :) > Is it making sense now ? ;) It did, but only after studying this BlueFlame thingy ;) Thanks! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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