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Date: Thu, 30 Apr 2009 21:19:36 -0700 From: Andrew Dickinson <andrew@...dna.net> To: David Miller <davem@...emloft.net> Cc: jelaas@...il.com, netdev@...r.kernel.org Subject: Re: tx queue hashing hot-spots and poor performance (multiq, ixgbe) Adding a bit more info... I should add, the other 4 ksoftirqd tasklets _are_ running, they're just not busy. (In case that wasn't clear...) Also of note, I rebooted the box (after recompiling with NUMA off). This time when I push traffic through, only the even-ksoftirqd's were busy.. I then tweaked some of the ring settings via ethtool and suddenly the odd-ksoftirqd's became busy (and the even ones went idle). Thoughts? Suggestions? driver issue? I'm at 2.6.30-rc3. (BTW, I'm under the assumption that since only 4 (of 8) ksoftirqd's are busy that I still have room to make this box go faster). -A On Thu, Apr 30, 2009 at 4:53 PM, Andrew Dickinson <andrew@...dna.net> wrote: > OK... I've got some more data on it... > > I passed a small number of packets through the system and added a ton > of printks to it ;-P > > Here's the distribution of values as seen by > skb_rx_queue_recorded()... count on the left, value on the right: > 37 0 > 31 1 > 31 2 > 39 3 > 37 4 > 31 5 > 42 6 > 39 7 > > That's nice and even.... Here's what's getting returned from the > skb_tx_hash(). Again, count on the left, value on the right: > 31 0 > 81 1 > 37 2 > 70 3 > 37 4 > 31 6 > > Note that we're entirely missing 5 and 7 and that those interrupts > seem to have gotten munged onto 1 and 3. > > I think the voodoo lies within: > return (u16) (((u64) hash * dev->real_num_tx_queues) >> 32); > > David, I made the change that you suggested: > //hash = skb_get_rx_queue(skb); > return skb_get_rx_queue(skb) % dev->real_num_tx_queues; > > And now, I see a nice even mixing of interrupts on the TX side (yay!). > > However, my problem's not solved entirely... here's what top is showing me: > top - 23:37:49 up 9 min, 1 user, load average: 3.93, 2.68, 1.21 > Tasks: 119 total, 5 running, 114 sleeping, 0 stopped, 0 zombie > Cpu0 : 0.0%us, 0.0%sy, 0.0%ni, 99.3%id, 0.0%wa, 0.3%hi, 0.3%si, 0.0%st > Cpu1 : 0.0%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 4.3%hi, 95.7%si, 0.0%st > Cpu2 : 0.0%us, 0.0%sy, 0.0%ni, 99.7%id, 0.0%wa, 0.0%hi, 0.3%si, 0.0%st > Cpu3 : 0.0%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 4.3%hi, 95.7%si, 0.0%st > Cpu4 : 0.0%us, 0.0%sy, 0.0%ni, 99.3%id, 0.0%wa, 0.3%hi, 0.3%si, 0.0%st > Cpu5 : 0.0%us, 0.0%sy, 0.0%ni, 2.0%id, 0.0%wa, 4.0%hi, 94.0%si, 0.0%st > Cpu6 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st > Cpu7 : 0.0%us, 0.0%sy, 0.0%ni, 5.6%id, 0.0%wa, 2.3%hi, 92.1%si, 0.0%st > Mem: 16403476k total, 335884k used, 16067592k free, 10108k buffers > Swap: 2096472k total, 0k used, 2096472k free, 146364k cached > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > 7 root 15 -5 0 0 0 R 100.2 0.0 5:35.24 > ksoftirqd/1 > 13 root 15 -5 0 0 0 R 100.2 0.0 5:36.98 > ksoftirqd/3 > 19 root 15 -5 0 0 0 R 97.8 0.0 5:34.52 > ksoftirqd/5 > 25 root 15 -5 0 0 0 R 94.5 0.0 5:13.56 > ksoftirqd/7 > 3905 root 20 0 12612 1084 820 R 0.3 0.0 0:00.14 top > <snip> > > > It appears that only the odd CPUs are actually handling the > interrupts, which doesn't jive with what /proc/interrupts shows me: > CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 > 66: 2970565 0 0 0 0 > 0 0 0 PCI-MSI-edge eth2-rx-0 > 67: 28 821122 0 0 0 > 0 0 0 PCI-MSI-edge eth2-rx-1 > 68: 28 0 2943299 0 0 > 0 0 0 PCI-MSI-edge eth2-rx-2 > 69: 28 0 0 817776 0 > 0 0 0 PCI-MSI-edge eth2-rx-3 > 70: 28 0 0 0 2963924 > 0 0 0 PCI-MSI-edge eth2-rx-4 > 71: 28 0 0 0 0 > 821032 0 0 PCI-MSI-edge eth2-rx-5 > 72: 28 0 0 0 0 > 0 2979987 0 PCI-MSI-edge eth2-rx-6 > 73: 28 0 0 0 0 > 0 0 845422 PCI-MSI-edge eth2-rx-7 > 74: 4664732 0 0 0 0 > 0 0 0 PCI-MSI-edge eth2-tx-0 > 75: 34 4679312 0 0 0 > 0 0 0 PCI-MSI-edge eth2-tx-1 > 76: 28 0 4665014 0 0 > 0 0 0 PCI-MSI-edge eth2-tx-2 > 77: 28 0 0 4681531 0 > 0 0 0 PCI-MSI-edge eth2-tx-3 > 78: 28 0 0 0 4665793 > 0 0 0 PCI-MSI-edge eth2-tx-4 > 79: 28 0 0 0 0 > 4671596 0 0 PCI-MSI-edge eth2-tx-5 > 80: 28 0 0 0 0 > 0 4665279 0 PCI-MSI-edge eth2-tx-6 > 81: 28 0 0 0 0 > 0 0 4664504 PCI-MSI-edge eth2-tx-7 > 82: 2 0 0 0 0 > 0 0 0 PCI-MSI-edge eth2:lsc > > > Why would ksoftirqd only run on half of the cores (and only the odd > ones to boot)? The one commonality that's striking me is that that > all the odd CPU#'s are on the same physical processor: > > -bash-3.2# cat /proc/cpuinfo | grep -E '(physical|processor)' | grep -v virtual > processor : 0 > physical id : 0 > processor : 1 > physical id : 1 > processor : 2 > physical id : 0 > processor : 3 > physical id : 1 > processor : 4 > physical id : 0 > processor : 5 > physical id : 1 > processor : 6 > physical id : 0 > processor : 7 > physical id : 1 > > I did compile the kernel with NUMA support... am I being bitten by > something there? Other thoughts on where I should look. > > Also... is there an incantation to get NAPI to work in the torvalds > kernel? As you can see, I'm generating quite a few interrrupts. > > -A > > > On Thu, Apr 30, 2009 at 7:08 AM, David Miller <davem@...emloft.net> wrote: >> From: Andrew Dickinson <andrew@...dna.net> >> Date: Thu, 30 Apr 2009 07:04:33 -0700 >> >>> I'll do some debugging around skb_tx_hash() and see if I can make >>> sense of it. I'll let you know what I find. My hypothesis is that >>> skb_record_rx_queue() isn't being called, but I should dig into it >>> before I start making claims. ;-P >> >> That's one possibility. >> >> Another is that the hashing isn't working out. One way to >> play with that is to simply replace the: >> >> hash = skb_get_rx_queue(skb); >> >> in skb_tx_hash() with something like: >> >> return skb_get_rx_queue(skb) % dev->real_num_tx_queues; >> >> and see if that improves the situation. >> > -- 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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