Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: The disappearing sys_call_table export. | From | Terje Eggestad <> | Date | 05 May 2003 12:12:23 +0200 |
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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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