kernel: mps0: Out of chain frames, consider increasing hw.mps.max_chains.

Scott Long scottl at
Tue Mar 8 18:34:32 UTC 2016

> On Mar 8, 2016, at 10:07 AM, Slawa Olhovchenkov <slw at> 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?


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