As you mentioned ESP driver, it declares .sg_tablesize = SG_ALL, so
BIO_VMERGE_BOUNDARY has no effect on the operation of this driver. Any
other driver where BIO_VMERGE_BOUNDARY does matter?
When BIO_VMERGE_BOUNDARY is turned on, requests that would not
otherwise fit into the device's limits, can.
Why would someone want to overshoot SG_ALL? ... and, shouldn't the
constant be increased then --- instead of making buggy BIO_VMERGE_BOUNDARY
expectations?
I'm talking about other devices, not about the ESP, here.
And which ones are those important drivers that need merge accounting?
A100U2W is an old card, I got it for $8.5 in bazaar, it does 38MB/s. This
virtual merge accounting helps to stuff on average 4 more segments into
the 32-entry table.
So the question is: to reduce number of requests by 12% on an outdated
SCSI card, it is sensible to maintain complicated merge accounting logic
in the core block layer? To me, it doesn't seem sensible.
Mikulas
--
To unsubscribe from this list: send the line "unsubscribe sparclinux" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
