Linux-kernel mailing list archive 2000-15,: Re: Asynch I/O overloaded 2.2.15/2.3.99

# Re: Asynch I/O overloaded 2.2.15/2.3.99

Jeff V. Merkey (jmerkey@timpanogas.com)
Tue, 11 Apr 2000 15:50:22 -0600

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I tries runs of 500 buffers, 1000 buffers, 2000 buffers, 3000 buffers,
and 4000 buffers.

And the winners are!

1. ll_rw_blk (and add_request/make_request) (oink, oink..... oink,
oink ... rooting around down in the hardware -- I think it's looking for
truffles)

and a close second:

2. ide_do_request
ide_delay_50ms (huge!!!)
ide_ioctl

I am also seeing an occasional Ooops when using **FULL** linux AIO (I
call ll_rw_blk and don't call wait on buffer, instead signal the NWFS
LRU directly from the b_end_io callback routine). Also, do I have to
call run_task_queue(&tq_disk) call all the time to get the AIO subsystem
to post the buffer-head request. If I don't call it, then the AIO's
just sit there and get processed about one every 10 seconds (???).

Jeff

Andi Kleen wrote:
>
> On Tue, Apr 11, 2000 at 05:05:39PM +0200, Andrea Arcangeli wrote:
> > >The main problem with the dentry and inode hashes is that they waste twice
> > >the memory they should (anchored list heads are *very* wasteful for hash
> > >tables). It is rather unlikely that the cost of the few saved if()s in the
> > >list macros weight up for the additional cache misses [patch will come
> > >as soon as I have tested it a bit more]
> >
> > You are perfectly right, but I really don't think it's for the speed but
> > for being allowed to use the list.h interface (at least that's why I used
> > the anchored list head in the write-COW fast path lookup of the
> > lvm-snapshot code even if I known I wasn't optimizing memory usage ;). I
> > strongly disagree in adding further by hand stuff like what we have just
> > for the buffer and page cache hashtables. We do need the same interface of
> > list.h _but_ that uses a single word sized head.
>
> Yes, I did a hlist[1] for this purpose. It does not have the 100% same interface
> because the semantics are a bit different.
>
> -Andi
>
> [1] suggestions for better names are welcome
>
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