We've already added ACPI_MUTEX and ACPI_SPINLOCK to ACPICA (split off from ACPI_SEMAPHORE), essentially at the request of Linux. I really would rather not add yet another type, for what looks like little gain. As far as portability, this is always an important issue for ACPICA. I am still getting complaints from other OSVs about the MUTEX and SPINLOCK types that were added. Bob >-----Original Message----- >From: Daniel Walker [mailto:dwalker@xxxxxxxxxx] >Sent: Monday, July 21, 2008 12:40 PM >To: Andi Kleen >Cc: Zhao, Yakui; linux-acpi@xxxxxxxxxxxxxxx; Ingo Molnar; Peter Zijlstra; >Brown, Len; Moore, Robert >Subject: Re: [PATCH 1/3] acpi: add real mutex function calls > >On Mon, 2008-07-21 at 21:20 +0200, Andi Kleen wrote: >> Daniel Walker wrote: >> > On Mon, 2008-07-21 at 09:51 +0800, Zhao Yakui wrote: >> >> On Sat, 2008-07-19 at 11:16 -0700, Daniel Walker wrote: >> >>> Instead of re-using semaphores for the mutex operation, I've >> >>> added usage of the kernel mutex for the os mutex implementation. >> >>> >> >> What is the advantage that the kernel mutex is used for the ACPI mutex >> >> implementation instead of using semaphore? >> >> And it seems that too much ACPICA source code is touched. >> > >> > In general you would want to use a mutex whenever your using mutex-like >> > semantics. If I see a mutex used in code then I have a pretty good idea >> > the locking is sane.. >> >> With a mutex the locking can be totally broken and with a semaphore the >> locking can be completely fine. They are both just tools which can be >> used correctly and also incorrectly. > >True .. > >> The main advantage of mutexes is that they can be slightly more >> efficient (doesn't matter for the ACPI case, the ACPI interpreter is not >> performance critical) and that they are easier to check with lockdep. >> But there are also other considerations like in ACPICA's case >portability. > >The ACPI interpreter actually specifically implements a mutex in the >AML. The interpreter wants a mutex, and not a semaphore. I'm not sure >why your bringing up portability issues .. > >> My feeling is that adding own semaphore wrappers to ACPICA wouldn't >> be an improvement. Defering to Bob Moore for his opinion, since >> he maintains ACPICA. > >I'm not trying to mod the locking that ACPI internally does (which I >think is mutex compatible) .. I'm just changing what the linux wrappers >are calling .. The additional lockdep calls are linux specific but they >aren't changing how the locking is already being done. > >Daniel -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
