[patch(?)] question wrt context switching during disk i/o

[Bill Wendling]

Also sprach Mike Galbraith:
} On Fri, 20 Oct 2000, Mark Hahn wrote:
} 
} > > This is something that has been bugging me for a while.  I notice
} > > on my system that during disk write we do much context switching,
} > > but not during disk read.  Why is that?
} > 
} > bdflush is broken in current kernels.  I posted to linux-mm about this,
} > but Rik et al haven't shown any interest.  I normally see bursts of 
} > up to around 40K cs/second when doing writes; I hacked a little 
} > premption counter into the kernel and verified that they're practially
} > all bdflush...
} 
There's some strangness in bdflush(). The comment says:

                /*
                 * If there are still a lot of dirty buffers around,
                 * skip the sleep and flush some more. Otherwise, we
                 * go to sleep waiting a wakeup.
                 */
                if (!flushed || balance_dirty_state(NODEV) < 0) {
                        run_task_queue(&tq_disk);
                        schedule();
                }

but the comment for balance_dirty_state() says:

/* -1 -> no need to flush
    0 -> async flush
    1 -> sync flush (wait for I/O completation) */
int balance_dirty_state(kdev_t dev)
{

Which leads me to believe that the `<' should be either `==' or `<='. I
tried it with the `<=' and it doesn't seem to be so bad...Here's a patch
to see if it helps you?

-- 
|| Bill Wendling                        [EMAIL PROTECTED]

--- linux/fs/buffer.c   Sat Oct 21 02:55:41 2000
+++ linux-2.4.0-test10pre4/fs/buffer.c  Sat Oct 21 12:27:10 2000
@@ -2683,7 +2683,7 @@
                 * skip the sleep and flush some more. Otherwise, we
                 * go to sleep waiting a wakeup.
                 */
-               if (!flushed || balance_dirty_state(NODEV) < 0) {
+               if (!flushed || balance_dirty_state(NODEV) <= 0) {
                        run_task_queue(&tq_disk);
                        schedule();
                }