Jan Kiszka wrote: > Philippe Gerum wrote: >> On Wed, 2010-04-14 at 01:05 +0200, Jan Kiszka wrote: >>> Philippe Gerum wrote: >>>> The steps now: >>>> >>>> - we implement the automatic switchback of shadow nrt threads to >>>> secondary mode, upon return from Xenomai (primary) syscalls. I am >>>> working on this. The most significant impact is on userland, due to the >>>> fastsynch support, actually. Kernel-wise, it's rather straightforward. >>>> The only exception to this would be when the caller owns an exclusive >>>> resource (like a mutex), in which case the mode downgrade should be >>>> postponed until the syscall releasing the last resource held returns. >>> Kernel is clear, but user space sounds indeed interesting. I guess we >>> need an out-of-band channel to tell the kernel about pending >>> user-space-only lock ownerships when calling some unrelated syscall. How >>> does your current approach look like? >> I want to keep things simple: shadow nrt will go through the syscalls >> for acquisition/release of owned resources, instead of fastsynchs. > > Then I'll have to pick this up as that will very likely create unhappy > customers. In fact, the majority of our Xenomai threads are nrt (yeah, > that happens if you convert existing applications).
Hmm, thinking about it again, there not that much to optimize in the trivial, non-nested locking case (on entry, we already go through the syscall if we aren't migrated yet, just the release syscall will be new). I will check what share of our load is nested and would actually suffer from unconditional syscalls. I just hope there is no issue with dropping the lazy scheme as that would complicate things in a way I would not want to go as well. Jan
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