On 04/24/2012 05:40 PM, Nicolas Pitre wrote: > On Tue, 24 Apr 2012, Andrew Haley wrote: > >> On 04/24/2012 05:18 PM, Jon Masters wrote: >>> I wasn't going to reply yet just due to lack of time and because Nico >>> covered the kernel helper stuff so well in his earlier posts. But just >>> to add, these kernel helpers have grown a little over time in higher >>> kernel revisions, but there is a mechanism to discover the revision >>> available (note: these are not VDSO but if it helps folks understand >>> them, think of them like that). They are the right way to solve the >>> atomics problem as best as we can for older devices. I believe the >>> correct thing to do is to get broken upstream projects to adopt generic >>> non-reimplemented-of-their-own routines that will transparently use the >>> kernel helpers if needed. >> >> But is that going to help me? Let's say I'm on an ARMv5 and need to >> do a longword operation. I can either use a lightweight spinlock or >> take the hit of a system call to do the cmpxchg8 operation. Am I >> really better off going into the kernel to do that? > > Absolutely! Because the kernel cmpxchg8 routine is _not_ a system call. > and it is going to be lighter than your custom solution with a lock. Okay, I think I see your point: you're going to use ldm/stm in the handler and detect an interrupt, then restart if necessary. Right, that may well be worth doing. I'll still need the locking fallback for old kernels, though. Andrew. _______________________________________________ arm mailing list arm@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/arm
