Messages in this thread | | | Date | Fri, 10 Feb 2012 22:39:02 +0200 | Subject | Re: [v7 0/8] Reduce cross CPU IPI interference | From | Gilad Ben-Yossef <> |
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On Fri, Feb 10, 2012 at 10:29 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > On Fri, 2012-02-10 at 22:13 +0200, Gilad Ben-Yossef wrote: >> My current understanding is that if I have a real time task and wish it >> have a deterministic performance time, you should call mlockall() to lock >> the program data and text into physical memory so that a less often taken >> branch or access to a new data region will not result in a page fault. >> >> You still have to worry about TLB misses on non hardware page table >> walk architecture, but at least everything is in the page tables >> >> If there is a better way to do this? I'm always happy to learn new >> ways to do things. :-) > > A rt application usually consists of a lot of non-rt parts and a usually > relatively small rt part. Using mlockall() pins the entire application > into memory, which while on the safe side is very often entirely too > much. > > The alternative method is to only mlock the text and data used by the rt > part. You need to be aware of what text runs in your rt part anyway, > since you need to make sure it is in fact deterministic code. > > One of the ways of achieving this is using a special linker section for > your vetted rt code and mlock()'ing only that text section. > > On thread creation, provide a custom allocated (and mlock()'ed) stack > etc.. > > Basically, if you can't tell a-priory what code is part of your rt part, > you don't have an rt part ;-) >
That I can totally agree with.
I guess mlockall() is still useful as a kind of hack for lazy people, although if you say that this kind of laziness does not really mix well with real time programming I will tend to agree... :-)
Gilad
-- Gilad Ben-Yossef Chief Coffee Drinker gilad@benyossef.com Israel Cell: +972-52-8260388 US Cell: +1-973-8260388 http://benyossef.com
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