From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Thu, 13 Oct 2011 15:49:23 +0100 Subject: [RFC/PATCH 5/7] ARM: Move get_thread_info macro definition to In-Reply-To: <20111013143420.GB21648@n2100.arm.linux.org.uk> References: <1317877714-11355-1-git-send-email-gdavis@mvista.com> <1317955121-28047-1-git-send-email-gdavis@mvista.com> <1317955121-28047-6-git-send-email-gdavis@mvista.com> <20111011095639.GB23848@arm.com> <20111012060433.GE188@mvista.com> <20111013143420.GB21648@n2100.arm.linux.org.uk> Message-ID: <20111013144923.GE6300@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Oct 13, 2011 at 03:34:20PM +0100, Russell King - ARM Linux wrote: > On Wed, Oct 12, 2011 at 02:04:33AM -0400, gdavis at mvista.com wrote: > > diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h > > index 78397d0..eaf4939 100644 > > --- a/arch/arm/include/asm/assembler.h > > +++ b/arch/arm/include/asm/assembler.h > > @@ -36,6 +36,20 @@ > > .endm > > #endif /* !CONFIG_THUMB2_KERNEL */ > > > > + .macro preempt_disable, tsk, cnt > > + get_thread_info \tsk > > + ldr \cnt, [\tsk, #TI_PREEMPT] > > + add \cnt, \cnt, #1 > > + str \cnt, [\tsk, #TI_PREEMPT] > > + .endm > > + > > + .macro preempt_enable, tsk, cnt > > + get_thread_info \tsk > > + ldr \cnt, [\tsk, #TI_PREEMPT] > > + sub \cnt, \cnt, #1 > > + str \cnt, [\tsk, #TI_PREEMPT] > > + .endm > > + > > /* > > * Endian independent macros for shifting bytes within registers. > > */ > > > > > > Not as efficient as it could be but I imagine the macros could > > be written to support optional load of \tsk and/or optional \tmp > > parameters to cover other common cases. > > It's actually not that simple either: if you disable preemption, then you > need to check for a preempt event after re-enabling preemption. That's not easily possible in assembly as calling a function would corrupt some registers. Is there any disadvantage with just doing the equivalent of preempt_enable_no_resched() for a few asm cases where this is needed? -- Catalin