Re: [andrea@suse.de: Re: generic rwsem [Re: Alpha "process table hang"]]
Linus Torvalds wrote: > For i386 and i486, there is no reason to try to maintain a complex fast > case. The machines are unquestionably going away - we should strive to not > burden them unnecessarily, but we should _not_ try to save two cycles. ... > Icache is also precious on the 386, which has no L2 in 99% of all cases. > Make it out-of-line. AFAIK, only some 386 clones have a cache -- the Intel ones do not. Therefore saving icache is not an issue, and the cycle cost of an out of line call is somewhat more than two cycles. -- Jamie - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [andrea@suse.de: Re: generic rwsem [Re: Alpha process table hang]]
Linus Torvalds wrote: For i386 and i486, there is no reason to try to maintain a complex fast case. The machines are unquestionably going away - we should strive to not burden them unnecessarily, but we should _not_ try to save two cycles. ... Icache is also precious on the 386, which has no L2 in 99% of all cases. Make it out-of-line. AFAIK, only some 386 clones have a cache -- the Intel ones do not. Therefore saving icache is not an issue, and the cycle cost of an out of line call is somewhat more than two cycles. -- Jamie - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [andrea@suse.de: Re: generic rwsem [Re: Alpha "process table hang"]]
On Fri, Apr 20, 2001 at 09:23:47AM +0100, David Howells wrote: > Andrea seems to have changed his mind on the non-inlining in the generic case. I changed my mind because if you benchmark the fast path you will do it without running out of icache (basically only down_* and up_* will be in the icache during the tight loop). And either ways shouldn't make a measurable difference in a real life benchmark. Andrea - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [andrea@suse.de: Re: generic rwsem [Re: Alpha "process table hang"]]
Linus Torvalds <[EMAIL PROTECTED]> wrote: > I think Andrea is right. Although this file seems to be entirely > old-fashioned and should never be used, right? I presume you're talking about "include/asm-i386/rwsem-spin.h"... If so, Andrea is right, there is a bug in it (repeated a number of times), though why the tests succeeded, I'm not sure. The file should only be used for the 80386 and maybe early 80486's where CMPXCHG doesn't work properly, everything above that can use the XADD implementation. > Also, I _really_ don't see why the code is inlined at all (in the real > . It shouldn't be. It should be a real function > call, and all be done inside lib/rwsem.c inside a > > #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK > > or whatever. Andrea seems to have changed his mind on the non-inlining in the generic case. But if you want it totally non-inline, then that can be done. However, whilst developing it, I did notice that that slowed things down, hence why I wanted it kept in line. I have some ideas on how to improve efficiency in that one anyway, based on some a comment from Alan Cox. > Please either set me straight, or send me a patch to remove > asm-i386/rwsem-spin.h and fix up linux/rwsem-spinlock.h. Ok? I think there are two seperate issues here: (1) asm-i386/rwsem-spin.h is wrong, and can probably be replaced with the generic spinlock implementation without inconveniencing people much. (though someone has commented that they'd want this to be inline as cycles are precious on the slow 80386). (2) "fix up linux/rwsem-spinlock.h": do you want the whole generic spinlock implementation made non-inline then? David - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [andrea@suse.de: Re: generic rwsem [Re: Alpha process table hang]]
Linus Torvalds [EMAIL PROTECTED] wrote: I think Andrea is right. Although this file seems to be entirely old-fashioned and should never be used, right? I presume you're talking about "include/asm-i386/rwsem-spin.h"... If so, Andrea is right, there is a bug in it (repeated a number of times), though why the tests succeeded, I'm not sure. The file should only be used for the 80386 and maybe early 80486's where CMPXCHG doesn't work properly, everything above that can use the XADD implementation. Also, I _really_ don't see why the code is inlined at all (in the real linux/rwsem-spinlock.h. It shouldn't be. It should be a real function call, and all be done inside lib/rwsem.c inside a #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK or whatever. Andrea seems to have changed his mind on the non-inlining in the generic case. But if you want it totally non-inline, then that can be done. However, whilst developing it, I did notice that that slowed things down, hence why I wanted it kept in line. I have some ideas on how to improve efficiency in that one anyway, based on some a comment from Alan Cox. Please either set me straight, or send me a patch to remove asm-i386/rwsem-spin.h and fix up linux/rwsem-spinlock.h. Ok? I think there are two seperate issues here: (1) asm-i386/rwsem-spin.h is wrong, and can probably be replaced with the generic spinlock implementation without inconveniencing people much. (though someone has commented that they'd want this to be inline as cycles are precious on the slow 80386). (2) "fix up linux/rwsem-spinlock.h": do you want the whole generic spinlock implementation made non-inline then? David - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [andrea@suse.de: Re: generic rwsem [Re: Alpha process table hang]]
On Fri, Apr 20, 2001 at 09:23:47AM +0100, David Howells wrote: Andrea seems to have changed his mind on the non-inlining in the generic case. I changed my mind because if you benchmark the fast path you will do it without running out of icache (basically only down_* and up_* will be in the icache during the tight loop). And either ways shouldn't make a measurable difference in a real life benchmark. Andrea - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
