From: "H. Peter Anvin" <hpa@zytor.com>
To: Alexander Potapenko <glider@google.com>,
Paul McKenney <paulmck@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Dmitriy Vyukov <dvyukov@google.com>,
James Y Knight <jyknight@google.com>
Subject: Re: Potentially missing "memory" clobbers in bitops.h for x86
Date: Fri, 29 Mar 2019 13:52:33 -0700 [thread overview]
Message-ID: <8e32ab34-c14c-1ccb-76f9-0dcd729a0ef6@zytor.com> (raw)
In-Reply-To: <CAG_fn=WKA_4Vzsh6yH+=5TFv-EMrX87pr+2c_ANoH_MOVpbe1w@mail.gmail.com>
On 3/29/19 8:54 AM, Alexander Potapenko wrote:
>
>> Of course, this would force the compiler to actually compute the
>> offset, which would slow things down. I have no idea whether this
>> would be better or worse than just using the "memory" clobber.
> Just adding the "memory" clobber to clear_bit() changes sizes of 5
> kernel functions (the three mentioned above, plus hub_activate() and
> native_send_call_func_ipi()) by a small margin.
> This probably means the performance impact of this clobber is
> negligible in this case.
I would agree with that.
Could you perhaps verify whether or not any of the above functions
contains a currently manifest bug?
Note: the atomic versions of these functions obviously need to have
"volatile" and the clobber anyway, as they are by definition barriers
and moving memory operations around them would be a very serious error.
-hpa
next prev parent reply other threads:[~2019-03-29 20:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-28 14:14 Alexander Potapenko
2019-03-28 16:22 ` Paul E. McKenney
2019-03-29 15:54 ` Alexander Potapenko
2019-03-29 20:52 ` H. Peter Anvin [this message]
2019-03-29 21:09 ` Paul E. McKenney
2019-03-29 21:51 ` H. Peter Anvin
2019-03-29 22:05 ` Paul E. McKenney
2019-03-29 22:30 ` hpa
2019-04-01 10:53 ` Peter Zijlstra
2019-04-01 15:44 ` Paul E. McKenney
2019-04-01 16:04 ` Peter Zijlstra
2019-04-01 15:00 ` Alexander Potapenko
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