> -----Original Message----- > From: Jakub Kicinski <kuba@xxxxxxxxxx> > Sent: 2023年7月6日 2:11 > To: Wei Fang <wei.fang@xxxxxxx> > Cc: Andrew Lunn <andrew@xxxxxxx>; davem@xxxxxxxxxxxxx; > edumazet@xxxxxxxxxx; pabeni@xxxxxxxxxx; ast@xxxxxxxxxx; > daniel@xxxxxxxxxxxxx; hawk@xxxxxxxxxx; john.fastabend@xxxxxxxxx; > Shenwei Wang <shenwei.wang@xxxxxxx>; Clark Wang > <xiaoning.wang@xxxxxxx>; netdev@xxxxxxxxxxxxxxx; dl-linux-imx > <linux-imx@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; bpf@xxxxxxxxxxxxxxx > Subject: Re: [PATCH net 3/3] net: fec: increase the size of tx ring and update > thresholds of tx ring > > On Wed, 5 Jul 2023 06:20:26 +0000 Wei Fang wrote: > > > > In addtion, this patch also updates the tx_stop_threshold and the > > > > tx_wake_threshold of the tx ring. In previous logic, the value of > > > > tx_stop_threshold is 217, however, the value of tx_wake_threshold > > > > is 147, it does not make sense that tx_wake_threshold is less than > > > > tx_stop_threshold. > > > > > > What do these actually mean? I could imagine that as the ring fills > > > you don't want to stop until it is 217/512 full. There is then some > > > hysteresis, such that it has to drop below 147/512 before more can be > added? > > > > > You must have misunderstood, let me explain more clearly, the queue > > will be stopped when the available BDs are less than tx_stop_threshold > > (217 BDs). And the queue will be waked when the available BDs are > > greater than tx_wake_threshold > > (147 BDs). So in most cases, the available BDs are greater than > > tx_wake_threshold when the queue is stopped, the only effect is to delay > packet sending. > > In my opinion, tx_wake_threshold should be greater than > > tx_stop_threshold, we should stop queue when the available BDs are not > enough for a skb to be attached. > > And wake the queue when the available BDs are sufficient for a skb. > > But you shouldn't restart the queue for a single packet either. > Restarting for a single packet wastes CPU cycles as there will be much more > stop / start operations. Two large packets seem like the absolute minimum > reasonable wake threshold. > > Setting tx_stop_threshold to MAX_SKB_FRAGS doesn't seem right either, as > you won't be able to accept a full TSO frame. > Maybe I should keep the tx_stop_threshold unchanged, so that the queue is to be stopped if the available BDs is not enough for a full TSO frame to be attached. And then just change tx_wake_threshold to tx_stop_threshold + 1, which I think it's more reasonable. > Please split the change, the netdev_err_once() should be one patch and then > the change to wake thresh a separate one. Okay, thanks!
