On Mon, 2003-05-05 at 11:38, Arjan van de Ven wrote:
> On Mon, May 05, 2003 at 11:33:36AM +0200, Terje Eggestad wrote:
> > 1. performance is everything.
> > 2. We're making a MPI library, and as such we don't have any control
> > with the application.
> > 3a. The various hardware for cluster interconnect all work with DMA.
> > 3b. the performance loss from copying from a receive area to the
> > userspace buffer is unacceptable.
> > 3c. It's therefore necessary for HW to access user pages.
> > 4. In order to to 3, the user pages must be pinned down.
>
> see how AIO does this, and O_DIRECT, and rawio.
>
> They all have the same requirement and manage to cope.
Ok, I havn't actually checked the code , but no, they don't have the
same requirement. they pin and unpin the user space memory at the
beginning and and of the operations.
take aio pseudo code:
aio_write()
{
pinmem();
if (file)
add_write_to_disk_queue();
.
.
.
};
kernel_aio_completion_handler()
{
unpinmem();
send_completion_event_to_task();
};
-- _________________________________________________________________________Terje Eggestad mailto:terje.eggestad@scali.no Scali Scalable Linux Systems http://www.scali.com
Olaf Helsets Vei 6 tel: +47 22 62 89 61 (OFFICE) P.O.Box 150, Oppsal +47 975 31 574 (MOBILE) N-0619 Oslo fax: +47 22 62 89 51 NORWAY _________________________________________________________________________
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