On Wed, 2006-12-13 at 18:58 +0100, Jan Kiszka wrote:
> Hi,
>
> while disassembling that bug in start_kernel, I noticed that
> ipipe_lock_cpu(flags) is used in a suboptimal way in some
> ipipe_XXX_head() services, i.e. when the flags are actually of no
> interest. The compiler still generates the unneeded pushf/pop <reg>, and
> this in a hot-path.
>
> Attached patch should perform better. Lightly tested, but QEMU SMP still
> works here.
Merged, thanks.
>
> Jan
> plain text document attachment (avoid-ipipe_lock_cpu.patch)
> ---
> include/linux/ipipe.h | 8 ++++----
> kernel/ipipe/core.c | 8 ++++----
> 2 files changed, 8 insertions(+), 8 deletions(-)
>
> Index: linux-2.6.19/include/linux/ipipe.h
> ===================================================================
> --- linux-2.6.19.orig/include/linux/ipipe.h
> +++ linux-2.6.19/include/linux/ipipe.h
> @@ -471,18 +471,18 @@ static inline void ipipe_restore_pipelin
> static inline void ipipe_stall_pipeline_head(void)
> {
> ipipe_declare_cpuid;
> - unsigned long flags;
>
> - ipipe_lock_cpu(flags);
> + local_irq_disable_hw();
> + ipipe_load_cpuid();
> __set_bit(IPIPE_STALL_FLAG,
> &__ipipe_pipeline_head()->cpudata[cpuid].status);
> }
>
> static inline unsigned long ipipe_test_and_stall_pipeline_head(void)
> {
> - unsigned long flags;
> ipipe_declare_cpuid;
>
> - ipipe_lock_cpu(flags);
> + local_irq_disable_hw();
> + ipipe_load_cpuid();
> return __test_and_set_bit(IPIPE_STALL_FLAG,
> &__ipipe_pipeline_head()->cpudata[cpuid].status);
> }
>
> Index: linux-2.6.19/kernel/ipipe/core.c
> ===================================================================
> --- linux-2.6.19.orig/kernel/ipipe/core.c
> +++ linux-2.6.19/kernel/ipipe/core.c
> @@ -303,10 +303,10 @@ void fastcall ipipe_restore_pipeline_fro
> void ipipe_unstall_pipeline_head(void)
> {
> struct ipipe_domain *head;
> - unsigned long flags;
> ipipe_declare_cpuid;
>
> - ipipe_lock_cpu(flags);
> + local_irq_disable_hw();
> + ipipe_load_cpuid();
> head = __ipipe_pipeline_head();
> __clear_bit(IPIPE_STALL_FLAG, &head->cpudata[cpuid].status);
>
> @@ -323,9 +323,9 @@ void ipipe_unstall_pipeline_head(void)
> void fastcall __ipipe_restore_pipeline_head(struct ipipe_domain *head,
> unsigned long x)
> {
> ipipe_declare_cpuid;
> - unsigned long flags;
>
> - ipipe_lock_cpu(flags);
> + local_irq_disable_hw();
> + ipipe_load_cpuid();
>
> if (x) {
> #ifdef CONFIG_DEBUG_KERNEL
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--
Philippe.
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