Messages in this thread | | | Date | Sat, 31 Jul 1999 23:44:05 +0200 | From | Roger Larsson <> | Subject | Re: Scheduling latencies news: less RAM = less latency |
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Hi all,
It was not my profile, I only forwarded it to Benno. It was found on the list, as "Excessive System time in MSP kernel." And it was run on a 512 MB Dual Pentium(!) system. [Note: maximum memory on a (well, two) slow Pentium, but the timing for each function should be the same]
When I reported it I was running in Win95 I could not check out man readprofile (and I can not now either...)
I noted that I was guessing a little but the data did look like it was number of calls, label, average time (look at total line)... [I am in a process of moving all my lists from Win95 to Linux, but I am waiting for my ISP to add some mail accounts...]
I have a patch of my own, not related to data in the above thread, that measures the time from setting of current->need_resched to the actual (re)scheduling takes place. It also samples instruction pointer at jiffies and prints data in schedule() if latency is longer than 5 ms (i.e. definable) - and that happens a lot! [I have kept it private group since it is my first patch and I do not think that it is SMP safe... or safe in any other way...]
And the readprofile from the forwarded thread "matches" the data I get...
There are stuff that takes several jiffies before it reschedules... (PPro 180, 96MB)
Linus Torvalds says later in the tread: > Also, the si_meminfo() etc stuff is just ridiculous. It's not a question > of latency: it's a question of CPU usage. We need to just get rid of those > functions instead of hacking around them - regardless of whether you add > "reschedule" calls in them, they just eat too much CPU, plain and simple. > Again, please don't treat the symptoms - I will not accept patches that > just say "oh, this is crap, so let's reschedule a bit here". They need to > be fixed properly or not at all.
I fully agree!
But Ingos patches are a nice start - they show that it can be done!
/RogerL
Benno Senoner wrote: > > Hi folks, again news > > as Roger Larrson suspected, there are some parts in the kernel > which have a too long execution path: > On his PPro with 512MB RAM, d_lookup takes up to 80ms to execute ! > > (I put Roger's latency profiling patch on my page) >
--
The Internet interprets Windows as damage, and routes around it.
Roger Larsson Skellefteå Sweden
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