Jens,
As you know, for the last week or so I have been battling some
performance issues in XFS and 2.4.20-rc1. Well, we finally found
the culprit back in 2.4.20-pre2.
When the block highmem patch was included, it added highmem_io to the
scsi controller structure. This can only ever be set to one if
CONFIG_HIGHIO is set. Yet there are several spots in the scsi
code which test based on its value regardless.
/*
* we really want to use sg even for a single segment request,
* however some people just cannot be bothered to write decent
* driver code so we can't risk to break somebody making the
* assumption that sg requests will always contain at least 2
* segments. if the driver is 32-bit dma safe, then use sg for
* 1 entry anyways. if not, don't rely on the driver handling this
* case.
*/
if (count == 1 && !SCpnt->host->highmem_io) {
this_count = req->current_nr_sectors;
goto single_segment;
}
Running with 128M of memory I usually do not turn highmem on. Well
finally I did and my performance went from this:
Version 1.02a ------Sequential Create------ --------Random Create--------
burst.americas.sgi. -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
2 156 4 +++++ +++ 118 3 149 3 +++++ +++ 108 2
which is the worst I ever saw, to this:
Version 1.02a ------Sequential Create------ --------Random Create--------
burst.americas.sgi. -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
2 2732 81 +++++ +++ 1771 38 2555 86 +++++ +++ 1418 30
Jens, can you do something about this please?
Steve
p.s. You now owe me a week's consulting some time ;-)
--Steve Lord voice: +1-651-683-3511 Principal Engineer, Filesystem Software email: lord@sgi.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Fri Nov 15 2002 - 22:00:39 EST