From mboxrd@z Thu Jan 1 00:00:00 1970 From: Linus Torvalds Subject: Re: [PATCH 2/11] x86: convert to generic helpers for IPI function calls Date: Tue, 22 Apr 2008 12:03:04 -0700 (PDT) Message-ID: References: <1208890227-24808-1-git-send-email-jens.axboe@oracle.com> <1208890227-24808-3-git-send-email-jens.axboe@oracle.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Return-path: In-Reply-To: <1208890227-24808-3-git-send-email-jens.axboe@oracle.com> Sender: linux-kernel-owner@vger.kernel.org To: Jens Axboe Cc: linux-arch@vger.kernel.org, Linux Kernel Mailing List , npiggin@suse.de, peterz@infradead.org, sam@ravnborg.org, Ingo Molnar List-Id: linux-arch.vger.kernel.org [ Ingo added to cc, since this is x86-specific ] On Tue, 22 Apr 2008, Jens Axboe wrote: > +++ b/arch/x86/kernel/apic_32.c > @@ -1357,6 +1357,10 @@ void __init smp_intr_init(void) > > /* IPI for generic function call */ > set_intr_gate(CALL_FUNCTION_VECTOR, call_function_interrupt); > + > + /* IPI for single call function */ > + set_intr_gate(CALL_FUNCTION_SINGLE_VECTOR, > + call_function_single_interrupt); Ok, one more comment.. Why bother with separate vectors for this? Why not just make the single vector do void smp_call_function_interrupt(void) { ack_APIC_irq(); irq_enter(); generic_smp_call_function_single_interrupt(); generic_smp_call_function_interrupt(); #ifdef CONFIG_X86_32 __get_cpu_var(irq_stat).irq_call_count++; #else add_pda(irq_call_count, 1); #endif irq_exit(); } since they are both doing the exact same thing anyway? Do we really require us to be able to handle the "single" case _while_ a "multiple" case is busy? Aren't we running all of these things with interrupts disabled anyway, so that it cannot happen? Or is it just a performance optimization? Do we expect to really have so many of the multiple interrupts that it's expensive to walk the list just because we also had a single interrupt to another CPU? That sounds a bit unlikely, but if true, very interesting.. Inquiring minds want to know.. Linus From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:35605 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754166AbYDVTEa (ORCPT ); Tue, 22 Apr 2008 15:04:30 -0400 Date: Tue, 22 Apr 2008 12:03:04 -0700 (PDT) From: Linus Torvalds Subject: Re: [PATCH 2/11] x86: convert to generic helpers for IPI function calls In-Reply-To: <1208890227-24808-3-git-send-email-jens.axboe@oracle.com> Message-ID: References: <1208890227-24808-1-git-send-email-jens.axboe@oracle.com> <1208890227-24808-3-git-send-email-jens.axboe@oracle.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-arch-owner@vger.kernel.org List-ID: To: Jens Axboe Cc: linux-arch@vger.kernel.org, Linux Kernel Mailing List , npiggin@suse.de, peterz@infradead.org, sam@ravnborg.org, Ingo Molnar Message-ID: <20080422190304.mLDD_nE8vx0ZGGeiA_h9DrIDCu_p_jUWJ7ixb70n4vk@z> [ Ingo added to cc, since this is x86-specific ] On Tue, 22 Apr 2008, Jens Axboe wrote: > +++ b/arch/x86/kernel/apic_32.c > @@ -1357,6 +1357,10 @@ void __init smp_intr_init(void) > > /* IPI for generic function call */ > set_intr_gate(CALL_FUNCTION_VECTOR, call_function_interrupt); > + > + /* IPI for single call function */ > + set_intr_gate(CALL_FUNCTION_SINGLE_VECTOR, > + call_function_single_interrupt); Ok, one more comment.. Why bother with separate vectors for this? Why not just make the single vector do void smp_call_function_interrupt(void) { ack_APIC_irq(); irq_enter(); generic_smp_call_function_single_interrupt(); generic_smp_call_function_interrupt(); #ifdef CONFIG_X86_32 __get_cpu_var(irq_stat).irq_call_count++; #else add_pda(irq_call_count, 1); #endif irq_exit(); } since they are both doing the exact same thing anyway? Do we really require us to be able to handle the "single" case _while_ a "multiple" case is busy? Aren't we running all of these things with interrupts disabled anyway, so that it cannot happen? Or is it just a performance optimization? Do we expect to really have so many of the multiple interrupts that it's expensive to walk the list just because we also had a single interrupt to another CPU? That sounds a bit unlikely, but if true, very interesting.. Inquiring minds want to know.. Linus