Date: Tue, 26 Jan 2010 12:26:27 -0800 From: Marcel Moolenaar <xcllnt@mac.com> To: "M. Warner Losh" <imp@bsdimp.com> Cc: src-committers@freebsd.org, jhb@freebsd.org, svn-src-all@freebsd.org, attilio@freebsd.org, marcel@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r202889 - head/sys/kern Message-ID: <3023270A-755A-4BCF-AC9A-C1F290052279@mac.com> In-Reply-To: <20100126.130932.722022410132669562.imp@bsdimp.com> References: <3bbf2fe11001260058i65604619l664bd0e49c1dbbd@mail.gmail.com> <3bbf2fe11001260339u7a694069m6a2bb7e18b2c546a@mail.gmail.com> <C6A8F7A7-F0A9-4F63-B61E-DDC5332DC495@mac.com> <20100126.130932.722022410132669562.imp@bsdimp.com>
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On Jan 26, 2010, at 12:09 PM, M. Warner Losh wrote:
> cpu_switch(struct thread *old, struct thread *new, struct mutext *mtx)
> {
> /* Save the registers to the pcb */
> old->td_lock = mtx;
> #if defined(SMP) && defined(SCHED_ULE)
> /* s/long/int/ if sizeof(long) != sizeof(void *) */
> /* as we have no 'void *' version of the atomics */
> while (atomic_load_acq_long(&new->td_lock) == (long)&blocked_lock)
> continue;
> #endif
> /* Switch to new context */
> }
Ok. So this is what ia64 has already, except for the atomic_load()
in the while loop. Since td_lock is volatile, I don't think we need
atomic_load(). To be explicit, ia64 has:
old->td_lock = mtx;
#if defined(SCHED_ULE) && defined(SMP)
/* td_lock is volatile */
while (new->td_lock == &blocked_lock)
;
#endif
Am I right, or am I missing a critical aspect of using atomic load?
> I also think that we should have that code somewhere for reference.
Since ia64 has a C implementation of cpu_switch(), we could make
that the reference implementation?
--
Marcel Moolenaar
xcllnt@mac.com
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