Messages in this thread | | | Subject | Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch | From | Lee Revell <> | Date | Tue, 20 Jul 2004 02:59:29 -0400 |
| |
On Tue, 2004-07-20 at 02:12, Ingo Molnar wrote: > * Lee Revell <rlrevell@joe-job.com> wrote: > > > Does this scale in a linear fashion with respect to CPU speed? You > > mentioned you were testing on a 2Ghz machine, does 700 usecs on that > > translate to 2800 usecs on a 500Mhz box? > > given that this particular latency is dominated by cachemisses the DRAM > latency controls it too which is independent of CPU MHz. Wrt. cachemiss > costs, newer CPUs typically have twice the L2-cache line size (so it > takes more bus cycles to fetch it) - the improvements in bandwidth of > fetching a single line should offset most of this. DRAM latencies didnt > improve much in the past 10 years so that's almost a constant between a > 500MHz/100MHz(system-bus) vs. 2GHz/400MHz system. So i'd guesstimate a > 500 MHz box to do somewhere around 1000-1500 usecs. >
The particular system I am working with is a Via EPIA M-6000, which is quite new but has a 600Mhz CPU due to it being fanless. I would imagine this would put it closer to a 'modern system' in this regard, as it uses DDR266.
> > How much I/O do you allow to be in flight at once? It seems like by > > decreasing the maximum size of I/O that you handle in one interrupt > > you could improve this quite a bit. Disk throughput is good enough, > > anyone in the real world who would feel a 10% hit would just throw > > hardware at the problem. > > i'm not sure whether this particular value (max # of sg-entries per IO > op) is runtime tunable. Jens? Might make sense to enable elvtune-alike > tunability of this value.
Yes, this would be a nice improvement.
> > limiting the in-flight IO will only work with IDE/PATA that doesnt have > multiple commands in flight for a given disk. SATA and SCSI handles > multiple command completions per IRQ invocation so limiting the size of > a single IO op has less effect there. >
But the current behavior only causes latency problems for an IDE system, so if this were made runtime-tunable then it would only be an issue for SATA, right? This would cover 99.9% of audio users, who would gladly trade some disk throughput for lower latency. You can record a *lot* of tracks with even a few MB/s of disk throughput.
Lee
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |