freebsd stable - Mar 2016 - kernel: mps0: Out of chain frames, consider increasing hw.mps.max_chains.

On Mon, Mar 07, 2016 at 02:10:12PM +0300, Slawa Olhovchenkov wrote:
> > >>> 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.
I am play with max_chains and like significant cost of handling
max_chains: with 8192 system resonded badly vs 2048. Now try 3192,
response like with 2048.

> On Mar 8, 2016, at 10:07 AM, Slawa Olhovchenkov <slw at zxy.spb.ru>
wrote:
> 
> On Mon, Mar 07, 2016 at 02:10:12PM +0300, Slawa Olhovchenkov wrote:
> 
>>>>>> 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.
> 
> I am play with max_chains and like significant cost of handling
> max_chains: with 8192 system resonded badly vs 2048. Now try 3192,
> response like with 2048.
Hi, I?m not sure I understand what you?re saying.  You said that you tried 8192,
but the system still complained of being out of chain frames?  Now you are
trying fewer, only 3192?

Thanks,
Scott