Re: [PATCH] io stalls (was: -rc7 Re: Linux 2.4.21-rc6)

[Andrea Arcangeli]

On Tue, Jun 10, 2003 at 07:13:45PM -0400, Chris Mason wrote:
> On Mon, 2003-06-09 at 18:19, Andrea Arcangeli wrote:
> The avg throughput per process with vanilla rc7 is 3MB/s, the best I've
> been able to do was with nr_requests at higher levels was 1.3MB/s.  With
> smaller of iozone threads (10 and lower so far) I can match rc7 speeds,
> but not with 20 procs.

at least with my patches, I also made this change:

-#define ELV_LINUS_SEEK_COST    16
+#define ELV_LINUS_SEEK_COST    1

 #define ELEVATOR_NOOP                                                  \
 ((elevator_t) {                                                                \
@@ -93,8 +93,8 @@ static inline int elevator_request_laten

 #define ELEVATOR_LINUS                                                 \
 ((elevator_t) {                                                                \
-       2048,                           /* read passovers */            \
-       8192,                           /* write passovers */           \
+       128,                            /* read passovers */            \
+       512,                            /* write passovers */           \
                                                                        \

you didn't change the I/O scheduler at all compared to mainline, so
there can be quite a lot of difference in the bandwidth average per
process between my patches and mainline and your patches (unless you run
elvtune or unless you backed out the above).

Anyways the 130671 < 100, 0 < 200, 0 < 300, 0 < 400, 0 < 500 from your
patch sounds perfectly fair and that's unrelated to I/O scheduler and
size of runqueue. I believe the most interesting difference is the
blocking of tasks until the waitqueue is empty (i.e. clearing the
waitqueue-full bit only when nobody is waiting). That is the right thing
to do of course, that was a bug in my patch I merged by mistake from
Nick's original patch, and that I'm going to fix immediatly of course.

Andrea