Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751923AbaJOTdl (ORCPT ); Wed, 15 Oct 2014 15:33:41 -0400 Received: from mail-lb0-f177.google.com ([209.85.217.177]:55159 "EHLO mail-lb0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751106AbaJOTdk (ORCPT ); Wed, 15 Oct 2014 15:33:40 -0400 MIME-Version: 1.0 X-Originating-IP: [67.83.175.92] In-Reply-To: References: <1413380500-3914-1-git-send-email-patrick@parcs.ath.cx> From: Patrick Palka Date: Wed, 15 Oct 2014 15:33:18 -0400 Message-ID: Subject: Re: [PATCH] ring-buffer: use atomic_[set|clear]_mask in place of a cmpxchg loop To: Linux Kernel Mailing List Cc: Patrick Palka , Steven Rostedt , Ingo Molnar Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 15, 2014 at 3:08 PM, Patrick Palka wrote: > On Wed, Oct 15, 2014 at 9:41 AM, Patrick Palka wrote: >> Instead of open-coding the equivalent cmpxchg loop we can just use >> atomic_set_mask and atomic_clear_mask to atomically OR or AND >> the value in &buffer->record_disabled. >> >> Cc: Steven Rostedt >> Cc: Ingo Molnar >> Signed-off-by: Patrick Palka >> --- >> >> NB: I have only tested this patch on x86_64 by booting with >> CONFIG_RING_BUFFER_STARTUP_TEST=y. >> >> kernel/trace/ring_buffer.c | 16 ++-------------- >> 1 file changed, 2 insertions(+), 14 deletions(-) >> >> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c >> index 2d75c94..e15ce2a 100644 >> --- a/kernel/trace/ring_buffer.c >> +++ b/kernel/trace/ring_buffer.c >> @@ -3050,13 +3050,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_record_enable); >> */ >> void ring_buffer_record_off(struct ring_buffer *buffer) >> { >> - unsigned int rd; >> - unsigned int new_rd; >> - >> - do { >> - rd = atomic_read(&buffer->record_disabled); >> - new_rd = rd | RB_BUFFER_OFF; >> - } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd); >> + atomic_set_mask(RB_BUFFER_OFF, &buffer->record_disabled); >> } >> EXPORT_SYMBOL_GPL(ring_buffer_record_off); >> >> @@ -3073,13 +3067,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_record_off); >> */ >> void ring_buffer_record_on(struct ring_buffer *buffer) >> { >> - unsigned int rd; >> - unsigned int new_rd; >> - >> - do { >> - rd = atomic_read(&buffer->record_disabled); >> - new_rd = rd & ~RB_BUFFER_OFF; >> - } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd); >> + atomic_clear_mask(RB_BUFFER_OFF, &buffer->record_disabled); >> } >> EXPORT_SYMBOL_GPL(ring_buffer_record_on); >> >> -- >> 2.1.2.443.g670a3c1 >> > > It just occurred to me that atomic_clear_mask and atomic_set_mask > expect to take an int *, not an atomic_t *, so this patch is bogus... > Sorry for the noise. Uh, actually, the generic implementations of these functions (defined in include/asm-generic/atomic.h) _do_ take an atomic_t *. It's the specialized x86 definitions of these functions (defined in arch/x86/include/asm/atomic.h) that take (expect) an int *. So this patch is not bogus; the x86 specializations for atomic_clear_mask and atomic_set_mask are. I will try to fix this in a separate patch. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/