Thanks for the replies so far I will investigate further. Greg, the machines are virtualized on VMWare. ESX 5. 4 cores each with 16 cores.
Dave, I will have to more carefully read your email. Thank you for assuming there is a sound reason for us looking at this. There is'nt really I am following the EMC guide provided by them. Its autogenerated documenation and the consultant/SME does not know. Regards On 8 August 2012 16:08, Dave Costakos <david.costa...@gmail.com> wrote: > https://access.redhat.com/knowledge/solutions/15482 also has some good > (really good) information on this and some ways which are maybe easier to > understand and use. > > > On Wed, Aug 8, 2012 at 10:45 AM, Dave Costakos > <david.costa...@gmail.com>wrote: > >> I don't personally know of a simpler way to set IRQ affinity on Linux >> than turning off irqbalance and updating the >> /proc/irq/<IRQNUM>/smp_affinity file. I'm also not at all sure how pinning >> interrupts inside a virtual machine will really help you much unless you >> are really, really, really (3 reallys) sensitive to VM latency for that >> particular interrupt or you really, really, really want to keep your >> application from being interrupted by the kernel scheduler. If you are so >> sensitive, then there are probably numerous other things you could benefit >> from aside from IRQ pinning inside a VM. (like interrupt coalescing >> settings, using a physical machine instead of a virtual one, choosing the >> 'right' virtualized NIC driver by doing latency testing, using SRIOV >> network devices or other such items). >> >> Regardless of the motiviations which I'm sure are sound, here are what I >> hope are useful notes. It's been a while, but I think the masses will >> correct any of my errors faster than they can answer the question :D. >> >> The smp_affinity file for an IRQ is a hex bit mask. Each bit represents >> a CPU, so you can create a mask that identifies 1 or more CPUs. A mask of >> 'ffffffff' would represent all CPUs because all the bits would be 1. You >> can cat the file /proc/interrupts to see where interrupts have historically >> fallen on a per-cpu basis since the machine has been up to ensure your >> smp_affinity mask has worked. >> >> So, to set affinity on a 4 CPU system like you have, the most >> understandable way for me has been to convert a binary number to a hex >> number and echo that into your smp_affinity file for that IRQ. Presuming >> IRQ 93 and you wanted to allow interrupts to occur only on CPU 4, you might >> try this: >> >> # echo -e "obase=16 \n ibase=2 \n 1000 \n" | bc >> 8 >> # echo 08 > /proc/irq/93/smp_affinity >> >> Or this for CPU 0 and 2 >> # echo -e "obase=16 \n ibase=2 \n 101 \n" | bc >> 5 >> # echo 05 > /proc/irq/93/smp_affinity >> >> You could of course script all of this which is probably required since a >> reboot will forget all your interrupt pinning. >> >> >> >> >> >> >> >> On Tue, Aug 7, 2012 at 10:57 AM, Greg Swift <g...@nytefyre.net> wrote: >> >>> On Tue, Aug 7, 2012 at 7:51 AM, Gerhardus Geldenhuis >>> <gerhardus.geldenh...@gmail.com> wrote: >>> > Hi >>> > >>> > I am following an EMC Networker guide which is mentioning stopping >>> > irqbalance as a service and setting affnity for all network interfaces >>> that >>> > that is faster than 1Gb. >>> > >>> > This is not something I have done before so learning rapidly. >>> > >>> > The logic behind it seems fine, and the Red Hat guide seems to suggest >>> the >>> > same: >>> > >>> http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Performance_Tuning_Guide/s-cpu-irq.html >>> > >>> > However this guide is for 6 and I am using 5.8 so I am reading it with >>> a >>> > pinch of 5.8 salt. >>> > >>> > I have a number of questions: >>> > 1. The server in question is virtual. Logically it would seem that >>> setting >>> > CPU affinity on virtualized infrastructure would have the same effect >>> as on >>> > physical infrastructure. Valid assumption? >>> > >>> > 2. The server is provisioned with 4 cpu's each with 1 core. However cat >>> > /proc/irq/83/smp_affinity which is my interrupt for eth0 shows >>> > 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001 >>> > (with irqbalance turned off ) >>> > I am not yet completely clear on how the masking word and have yet to >>> find a >>> > cleIar explanation. This value is double the amount of cores I actually >>> > have. This is a bit confusing so any explanation would be appreciated. >>> > >>> > 3. Lastly how do I set affinity, although understanding q2 would >>> answer q3? >>> > I am happy to reread any documentation. The man 5 proc was not detailed >>> > enough and I found the above mentioned Red Hat guide also lacking in >>> > clarity. >>> > >>> > Disclaimer: Still suffering from the effects of a server bout of man >>> flu so >>> > any lack of clarity might be entirely down to me.... >>> >>> I haven't actually done what you are talking about, however I'm >>> curious if there might be a simpler way. >>> >>> The host machine for that virtual is which hypervisor? How many CPUs >>> (real vs HT etc)? >>> >>> -greg >>> >>> _______________________________________________ >>> rhelv5-list mailing list >>> rhelv5-list@redhat.com >>> https://www.redhat.com/mailman/listinfo/rhelv5-list >>> >> >> >> >> -- >> Dave Costakos >> mailto:david.costa...@gmail.com >> > > > > -- > Dave Costakos > mailto:david.costa...@gmail.com > > _______________________________________________ > rhelv5-list mailing list > rhelv5-list@redhat.com > https://www.redhat.com/mailman/listinfo/rhelv5-list > -- Gerhardus Geldenhuis
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