Re: [Myrinet] DMA related question.
Moon-Sang Lee <[email protected]>
| Newsgroups | gmane.network.myrinet.general |
|---|---|
| Message-ID | <[email protected]> |
Hello, On Sat, Apr 13, 2002 at 12:20:37AM -0400, Saurabh Agarwal wrote: > Hi, > > In MCP, Is it possible to write 2 separate pinned memory > locations (in host memory) using a single DMA call ? Both the > updates are writing very small, immediate data. If not, is > their any other way by which we can update these two values > without having to incur 2 separate DMA costs ? Myrinet NIC supports the chained DMA mechanism, thus you can make two DMA blocks that are going to upload the separate data to each pinned memory locations with a single DMA start. Refer to MCP programmer's guide from Myricom homepage. >I read something > about use of a PIO but am not too clear on it yet !. Could someone > please help in telling weather a PIO could be used along with > a DMA and will it help amortizing some overhead ? What is the > typical latency for a PIO call that will write, lets say, 4 bytes ? > If there is a pointer which can explain how to use PIOs, > it would be really helpful. > PIO could reduce the latency, but it increases the overhead of host processor. We need to sophisticate the mixed use of DMA and PIO considering the communication to commputation ratio. Anyway, a user process which will use PIO should have the mapping from virtual address to physical address. Refer to mmap system call to know how to remap the virtual address, or why don't you read the GM source code? :) Regards, sang > Thanks for your time, > Regards, > --Saurabh > > > *************************************************************************** > Graduate Student 445 Waupelani Drive (R) 814-278-9272 > C.S.E Department Apt# H-21 [email protected] > Penn State University State College > PA - 16801 http://www.cse.psu.edu/~sagarwal > *************************************************************************** > > _______________________________________________ > Myrinet mailing list > [email protected] > http://email.osc.edu/mailman/listinfo/myrinet ------------Korea Advanced Institute of Science and Technology------------- Moon-Sang Lee [email protected] CS dept. KAIST +82-42-869-5585@calab Sarang Kwan. 524 +82-42-879-4145@dormitory Homepage URL http://camars.kaist.ac.kr/~mslee ---------------------Computer Architecture Laboratory----------------------