Increasing MAXPHYS

[Alexander Motin]

Julian Elischer wrote:
> In the Fusion-io driver we find that the limiting factor is not the
> size of MAXPHYS, but the fact that we can not push more than
> 170k tps through geom. (in my test machine. I've seen more on some
> beefier machines), but that is only a limit on small transacrtions,
> or in the case of large transfers the DMA engine tops out before a
> bigger MAXPHYS would make any difference.

Yes, GEOM is quite CPU-hungry on high request rates due to number of
context switches. But impact probably may be reduced from two sides: by
reducing overhead per request, or by reducing number of requests. Both
ways may give benefits.

If common opinion is not to touch defaults now - OK, agreed. (Note,
Scott, I have agreed :)) But returning to the original question, does
somebody knows real situation when increased MAXPHYS still causes
problems? At least to make it safe.

-- 
Alexander Motin