From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Nicholas Piggin <npiggin@gmail.com>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [RFC PATCH 2/2] powerpc: nop trap instruction after WARN_ONCE fires
Date: Fri, 23 Sep 2022 16:47:20 +0000 [thread overview]
Message-ID: <264df1e7-ad54-0fa3-c658-dff76dec8a97@csgroup.eu> (raw)
In-Reply-To: <20220923154143.1115645-2-npiggin@gmail.com>
Le 23/09/2022 à 17:41, Nicholas Piggin a écrit :
> WARN_ONCE and similar are often used in frequently executed code, and
> should not crash the system. The program check interrupt caused by
> WARN_ON_ONCE can be a significant overhead even when nothing is being
> printed. This can cause performance to become unacceptable, having the
> same effective impact to the user as a BUG_ON().
>
> Avoid this overhead by patching the trap with a nop instruction after a
> "once" trap fires. Conditional warnings that return a result must have
> equivalent compare and branch instructions after the trap, so when it is
> nopped the statement will behave the same way. It's possible the asm
> goto should be removed entirely and this comparison just done in C now.
You mean, just like PPC32 ? (Since db87a7199229 ("powerpc/bug: Remove
specific powerpc BUG_ON() and WARN_ON() on PPC32"))
But I'm having hard time with your change.
You change only WARN_ON()
But WARN_ON_ONCE() calls __WARN_FLAGS()
And WARN_ONCE() calls WARN() via DO_ONCE_LITE_IF()
So I don't see any ..._ONCE something going with WARN_ON().
Am I missing something ?
Otherwise, what you want to do is to patch the 'twi' in __WARN_FLAGS()
by a non conditional branch to __label_warn_on .
Christophe
next prev parent reply other threads:[~2022-09-23 16:48 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-23 15:41 [RFC PATCH 1/2] powerpc: Don't use extable for WARN Nicholas Piggin
2022-09-23 15:41 ` [RFC PATCH 2/2] powerpc: nop trap instruction after WARN_ONCE fires Nicholas Piggin
2022-09-23 16:47 ` Christophe Leroy [this message]
2022-10-04 4:31 ` Nicholas Piggin
2022-10-04 8:14 ` Christophe Leroy
2022-09-26 8:56 ` David Laight
2022-09-23 15:49 ` [RFC PATCH 1/2] powerpc: Don't use extable for WARN Christophe Leroy
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