Re: Add extra_buff_count flag

[Radha Ramachandran <radha@google.com>]

Thank you for the documentation update.

You also mentioned that you saw some kind of a race on io_u->flags
today, do you by any chance know if you were using iodepth_low or
iodepth_batch_complete or libaio engine options.
I think I see an issue when using them and understand why it happens,
but dont have a clean fix yet, will hopefully have one soon. I was
wondering if its the same issue you are seeing.
Basically the issue is we might think the queue is full (because we
cannot allocate any more io_u (they are probably doing async verify)),
but the code assumes that if the queue is full, then there is atleast
one I/O that we can do "io_getevents" on. And that will cause a hang
in the code.

thanks
-radha


On Wed, Nov 4, 2009 at 11:22 AM, Jens Axboe <jens.axboe@oracle.com> wrote:
> On Wed, Nov 04 2009, Jens Axboe wrote:
>> On Wed, Nov 04 2009, Radha Ramachandran wrote:
>> > I would rather document it than add it by default in case it starts
>> > hitting memory constraints because its allocating more memory buffers.
>>
>> Yes I agree, I usually don't like having one option implying changes for
>> another either.
>
> So the problem with documentation is that usually nobody reads it. This
> is what the HOWTO/man page currently has:
>
> verify_async=int        Fio will normally verify IO inline from the submitting
>                thread. This option takes an integer describing how many
>                async offload threads to create for IO verification instead,
>                causing fio to offload the duty of verifying IO contents
>                to one or more separate threads. If using this offload
>                option, even sync IO engines can benefit from using an
>                iodepth setting higher than 1, as it allows them to have
>                IO in flight while verifies are running.
>
> It's already documented...
>
> --
> Jens Axboe
>
>