> On Mar 6, 2016, at 10:04 PM, Slawa Olhovchenkov <s...@zxy.spb.ru> wrote: > > On Sun, Mar 06, 2016 at 06:20:06PM -0800, Scott Long wrote: > >> >>> On Mar 6, 2016, at 1:27 PM, Slawa Olhovchenkov <s...@zxy.spb.ru> wrote: >>> >>> On Sun, Mar 06, 2016 at 01:10:42PM -0800, Scott Long wrote: >>> >>>> Hi, >>>> >>>> The message is harmless, it's a reminder that you should tune the kernel >>>> for your workload. When the message is triggered, it means that a >>>> potential command was deferred, likely for only a few microseconds, and >>>> then everything moved on as normal. >>>> >>>> A command uses anywhere from 0 to a few dozen chain frames per I/o, >>>> depending on the size of the io. The chain frame memory is allocated at >>>> boot so that it's always available, not allocated on the fly. When I >>>> wrote this driver, I felt that it would be wasteful to reserve memory for >>>> a worst case scenario of all large io's by default, so I put in this >>>> deferral system with a console reminder to for tuning. >>>> >>>> Yes, you actually do have 900 io's outstanding. The controller buffers >>>> the io requests and allows the system to queue up much more than what sata >>>> disks might allow on their own. It's debatable if this is good or bad, >>>> but it's tunable as well. >>>> >>>> Anyways, the messages should not cause alarm. Either tune up the chain >>>> frame count, or tune down the max io count. >>> >>> I am don't know depends or not, but I see dramaticaly performance drop >>> at time of this messages. >>> >> >> Good to know. Part of the performance drop might be because of the slowness >> of printing to the console. > > no, on console print may be one per minute >
The one-per-minute prints are by design. I should probably make it print once and then increment a sysctl counter. >>> How I can calculate buffers numbers? >> >> If your system is new enough to have mpsutil, please run it ‘mpsutil >> show iocfacts’. > > As I see mpsutil present only on -HEAD. > Can I compile it on 10-STABLE? > Yes, I believe it should compile on 10, but I have not tried it recently. >> If not, then boot your system with bootverbose and send me the output. > > I can do this day ago. > >>> I am have very heavy I/O. >> >> Out of curiosity, do you redefine MAXPHYS/DFLTPHYS in your kernel config? > > no > >>> This allocated one for all controllers, or allocated for every controller? >> >> It’s per-controller. >> >> I’ve thought about making the tuning be dynamic at runtime. I >> implemented similar dynamic tuning for other drivers, but it seemed >> overly complex for low benefit. Implementing it for this driver >> would be possible but require some significant code changes. > > What cause of chain_free+io_cmds_active << max_chains? > One cmd can use many chains? Yes. A request uses and active command, and depending on the size of the I/O, it might use several chain frames. Scott _______________________________________________ freebsd-stable@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
