Interesting thread on comp.arch newsgroup today... >>See if anyone can figure this one out: >> >>I have a colleague who is running a C program he wrote on a brand new >>dell PC. The program involves reading and writing a lot of data across >>the PCI interface to a peripheral card. >> >>The strange thing is that his program runs markedly faster when he >>opens Windows Media Player. I didn't believe him at first, but I've >>seen the effect first hand. If there's enough interest I might see if >>he's willing to measure the speed-up ratio. >> >>Anyone able to think of what this might be? Educated speculation >>welcome... >Timer interupt latency. Windows normally has a interrupt rate of 100Hz or or >possibly 64Hz depending on the hardware time source (unless it's windows 98 >which is 200Hz). However this is dynamically variable via the MultiMedia >Timer API. When you open Windows MediaPlayer it will increase the timer rate >to 1000 or 1024Hz again depending on the time source. > >Exactly the same thing can be seen if you install the Quicktime and have it >resident in the system tray even if you don't open the player. > >The increase in the timer rate will have some side effects with when things >are reported back to the driver that is transfering data, how often the >schedular is invoked and how long IOComplete might block for etc. > >I suspect that the application is performing lots of smallish transfers >rather than a few huge ones otherwise you shouldn't see the effect. > >See ><http://www.vmware.com/pdf/vmware_timekeeping.pdf>http://www.vmware.com/pdf/vmware_timekeeping.pdf > >for a discussion of >this and what a nightmare it is for keeping correct time in VMWare virtual >machines
James Lux, P.E. Spacecraft Radio Frequency Subsystems Group Flight Communications Systems Section Jet Propulsion Laboratory, Mail Stop 161-213 4800 Oak Grove Drive Pasadena CA 91109 tel: (818)354-2075 fax: (818)393-6875 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachments/20060420/347f5033/attachment.htm
