Date: Wed, 10 Dec 2003 11:49:57 -0500 From: Mathew Kanner <mat@cnd.mcgill.ca> To: Ian Freislich <ianf@za.uu.net> Cc: freebsd-current@freebsd.org Subject: Re: Why are sound ioctl calls so slow? Message-ID: <20031210164957.GJ11072@cnd.mcgill.ca> In-Reply-To: <49687.1071043939@za.uu.net> References: <20031209192557.GE11072@cnd.mcgill.ca> <49687.1071043939@za.uu.net>
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On Dec 10, Ian Freislich wrote: > Mathew Kanner wrote: > > > 3224 mpg123 0.000748 CALL ioctl(0x3,SNDCTL_DSP_SETFMT,0xbfbff834) > > > 3224 mpg123 0.026260 RET ioctl 0 > > > > > > Can someone firstly tell me whether or not if it is reasonable to > > > expect the ioctl call to be any faster. Perhaps my reasoning is > > > flawed, but I'd expect about 61000 instructions to be executed by > > > the CPU (133MHz) in 23ms at an average of 50 clock cycles per > > > instruction not taking cache misses into account. I cannot concieve > > > of any reason why it should take 61000 instructions to write the > > > format, speed or stereo to the sound hardware. > > > > > > Does each ioctl result in a context switch which means that the cpu > > > spends time on other processes for each ioctl call? I'm not sure > > > that this is what happens because mpg123 uses 100% cpu for about > > > 10 seconds and then settles down to about 40% once it actually > > > starts decoding the mp3. > > > > Ian, > > Sounds like you understand the problem, maybe you should > > investigate :) > > Hmm, I was hoping someone familiar with the sound stuff would be > able to say whether I was smoking my socks or not. You aren't gonna find it. > This is very > uncharted territory for me. I'll try to have a look and see if I > can figure out what gives this week end. > > > My first guess would be the device is rebuilding feeder/mixer > > chains every time mpg123 changes format. I would run the test one > > more time, disabling vchans and rate conversion. > > > > sysctl hw.snd.report_soft_formats=0 hw.snd.maxautovchans=0 > > That didn't make a (noticeable) difference: > > 4090 mpg123 0.000603 CALL ioctl(0x3,SNDCTL_DSP_STEREO,0xbfbff864) > 4090 mpg123 0.026047 RET ioctl 0 > 4090 mpg123 0.000582 CALL ioctl(0x3,SNDCTL_DSP_SPEED,0xbfbff864) > 4090 mpg123 0.017735 RET ioctl 0 > 4090 mpg123 0.000414 CALL ioctl(0x3,SNDCTL_DSP_SETFMT,0xbfbff864) > 4090 mpg123 0.026004 RET ioctl 0 You complained that mpg123 was doing hundered of system calls. Did that remain constant aswell? > > > I didn't notice which version of fbsd that you are using. > > 5.2-CURRENT (2003-10-21 00:00:00 GMT) and 4.9-STABLE. --Mat -- The state has no business in the bedrooms of the nation. - Pierre Elliott Trudeau
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