Linus Torvalds <torvalds@transmeta.com> writes:
> I wonder if you're getting screwed by bdflush().. You do have a lot of
> context switching going on, and you do have a clear pattern: once the
> write-out gets going, you're filling new cached pages at about the same
> pace that you're writing them out, which definitely means that the dirty
> buffer balancing is nice and active.
>
Yes, but things are similar when I finally allocate whole memory, and
kswapd kicks in. Everything is behaving in the same way, so it is
definitely not the VM, as you pointed out.
> So the problem is that you're obviously not actually getting the
> throughput you should - it's not the VM, as the page cache grows nicely at
> the same rate you're writing.
>
Yes.
> Try something for me: in fs/buffer.c make "balance_dirty_state()" never
> return > 0, ie make the "return 1" be a "return 0" instead.
>
Sure. I recompiled fresh 2.4.13 at the work an rerun tests. This time
on different setup, so numbers are even smaller (tests were performed
at the last partition of the disk, where disk is capable of ~ 13MB/s)
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
1 0 0 0 6308 600 441592 0 0 0 7788 159 132 0 7 93
0 1 0 0 3692 580 444272 0 0 0 5748 169 197 1 4 95
0 1 0 0 3180 556 444804 0 0 0 5632 228 408 1 5 94
0 1 0 0 3720 556 444284 0 0 0 7672 226 418 3 4 93
0 1 0 0 3836 556 444148 0 0 0 5928 249 509 0 8 92
0 1 0 0 3204 388 444952 0 0 0 7828 156 139 0 6 94
1 1 0 0 3456 392 444692 0 0 0 5952 157 139 0 5 95
0 1 0 0 3728 400 444428 0 0 0 7840 312 750 0 7 93
0 1 0 0 3968 404 444168 0 0 0 5952 216 364 0 5 95
> That will cause us to not wake up bdflush at all, and if you're just on
> the "border" of 40% dirty buffer usage you'll have bdflush work in
> lock-step with you, alternately writing out buffers and waiting for them.
>
> Quite frankly, just the act of doing the "write_some_buffers()" in
> balance_dirty() should cause us to block much better than the synchronous
> waiting anyway, because then we will block when the request queue fills
> up, not at random points.
>
> Even so, considering that you have such a steady 9-10MB/s, please double-
> check that it's not something even simpler and embarrassing, like just
> having forgotten to enable auto-DMA in the kernel config ;)
>
Yes, I definitely have DMA turned ON. All parameters are OK. :)
# hdparm /dev/hda
/dev/hda:
multcount = 16 (on)
I/O support = 0 (default 16-bit)
unmaskirq = 0 (off)
using_dma = 1 (on)
keepsettings = 0 (off)
nowerr = 0 (off)
readonly = 0 (off)
readahead = 8 (on)
geometry = 1650/255/63, sectors = 26520480, start = 0
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This archive was generated by hypermail 2b29 : Wed Oct 31 2001 - 21:00:26 EST