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From: "Luck, Tony" <tony.luck@intel.com>
To: Mateusz Guzik <mjguzik@gmail.com>,
	"Torvalds, Linus" <torvalds@linux-foundation.org>
Cc: "catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"jan.glauber@gmail.com" <jan.glauber@gmail.com>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"mpe@ellerman.id.au" <mpe@ellerman.id.au>,
	"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"will@kernel.org" <will@kernel.org>
Subject: RE: [PATCH] lockref: stop doing cpu_relax in the cmpxchg loop
Date: Fri, 13 Jan 2023 21:47:50 +0000	[thread overview]
Message-ID: <SJ1PR11MB6083B48A2B2114EF833D69E2FCC29@SJ1PR11MB6083.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20230113184447.1707316-1-mjguzik@gmail.com>

> diff --git a/lib/lockref.c b/lib/lockref.c
> index 45e93ece8ba0..2afe4c5d8919 100644
> --- a/lib/lockref.c
> +++ b/lib/lockref.c
> @@ -23,7 +23,6 @@
>               }                                                               \
>               if (!--retry)                                                   \
>                       break;                                                  \
> -             cpu_relax();                                                    \
>       }                                                                       \
>  } while (0)

The computer necrophiliacs at Debian and Gentoo seem determined
to keep ia64 alive.

So perhaps this should s/cpu_relax/soemt_relax/ where soemt_relax
is a no-op everywhere except ia64, which can define it as cpu_relax.

The ia64 case is quite painful if one thread on a core is spinning in that
loop, while the other thread on the same core is the one that needs to
run to update that value so that the cmpxchg can succeed.

-Tony

WARNING: multiple messages have this Message-ID (diff)
From: "Luck, Tony" <tony.luck@intel.com>
To: Mateusz Guzik <mjguzik@gmail.com>,
	"Torvalds, Linus" <torvalds@linux-foundation.org>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"will@kernel.org" <will@kernel.org>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"jan.glauber@gmail.com" <jan.glauber@gmail.com>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: RE: [PATCH] lockref: stop doing cpu_relax in the cmpxchg loop
Date: Fri, 13 Jan 2023 21:47:50 +0000	[thread overview]
Message-ID: <SJ1PR11MB6083B48A2B2114EF833D69E2FCC29@SJ1PR11MB6083.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20230113184447.1707316-1-mjguzik@gmail.com>

> diff --git a/lib/lockref.c b/lib/lockref.c
> index 45e93ece8ba0..2afe4c5d8919 100644
> --- a/lib/lockref.c
> +++ b/lib/lockref.c
> @@ -23,7 +23,6 @@
>               }                                                               \
>               if (!--retry)                                                   \
>                       break;                                                  \
> -             cpu_relax();                                                    \
>       }                                                                       \
>  } while (0)

The computer necrophiliacs at Debian and Gentoo seem determined
to keep ia64 alive.

So perhaps this should s/cpu_relax/soemt_relax/ where soemt_relax
is a no-op everywhere except ia64, which can define it as cpu_relax.

The ia64 case is quite painful if one thread on a core is spinning in that
loop, while the other thread on the same core is the one that needs to
run to update that value so that the cmpxchg can succeed.

-Tony

WARNING: multiple messages have this Message-ID (diff)
From: "Luck, Tony" <tony.luck@intel.com>
To: Mateusz Guzik <mjguzik@gmail.com>,
	"Torvalds, Linus" <torvalds@linux-foundation.org>
Cc: "catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"jan.glauber@gmail.com" <jan.glauber@gmail.com>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"mpe@ellerman.id.au" <mpe@ellerman.id.au>,
	"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"will@kernel.org" <will@kernel.org>
Subject: RE: [PATCH] lockref: stop doing cpu_relax in the cmpxchg loop
Date: Fri, 13 Jan 2023 21:47:50 +0000	[thread overview]
Message-ID: <SJ1PR11MB6083B48A2B2114EF833D69E2FCC29@SJ1PR11MB6083.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20230113184447.1707316-1-mjguzik@gmail.com>

> diff --git a/lib/lockref.c b/lib/lockref.c
> index 45e93ece8ba0..2afe4c5d8919 100644
> --- a/lib/lockref.c
> +++ b/lib/lockref.c
> @@ -23,7 +23,6 @@
>               }                                                               \
>               if (!--retry)                                                   \
>                       break;                                                  \
> -             cpu_relax();                                                    \
>       }                                                                       \
>  } while (0)

The computer necrophiliacs at Debian and Gentoo seem determined
to keep ia64 alive.

So perhaps this should s/cpu_relax/soemt_relax/ where soemt_relax
is a no-op everywhere except ia64, which can define it as cpu_relax.

The ia64 case is quite painful if one thread on a core is spinning in that
loop, while the other thread on the same core is the one that needs to
run to update that value so that the cmpxchg can succeed.

-Tony

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2023-01-13 21:48 UTC|newest]

Thread overview: 108+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-12 23:36 lockref scalability on x86-64 vs cpu_relax Mateusz Guzik
2023-01-13  0:13 ` Linus Torvalds
2023-01-13  0:13   ` Linus Torvalds
2023-01-13  0:13   ` Linus Torvalds
2023-01-13  0:30   ` Luck, Tony
2023-01-13  0:30     ` Luck, Tony
2023-01-13  0:30     ` Luck, Tony
2023-01-13  0:45     ` Linus Torvalds
2023-01-13  0:45       ` Linus Torvalds
2023-01-13  0:45       ` Linus Torvalds
2023-01-13  7:55     ` ia64 removal (was: Re: lockref scalability on x86-64 vs cpu_relax) Ard Biesheuvel
2023-01-13  7:55       ` Ard Biesheuvel
2023-01-13  7:55       ` Ard Biesheuvel
2023-01-13 16:17       ` Luck, Tony
2023-01-13 16:17         ` Luck, Tony
2023-01-13 16:17         ` Luck, Tony
2023-01-13 20:49       ` Jessica Clarke
2023-01-13 20:49         ` Jessica Clarke
2023-01-13 20:49         ` Jessica Clarke
2023-01-13 21:03         ` Luck, Tony
2023-01-13 21:03           ` Luck, Tony
2023-01-13 21:03           ` Luck, Tony
2023-01-13 21:04           ` Jessica Clarke
2023-01-13 21:04             ` Jessica Clarke
2023-01-13 21:04             ` Jessica Clarke
2023-01-13 21:05       ` John Paul Adrian Glaubitz
2023-01-13 21:05         ` John Paul Adrian Glaubitz
2023-01-13 21:05         ` John Paul Adrian Glaubitz
2023-01-13 23:25         ` Ard Biesheuvel
2023-01-13 23:25           ` Ard Biesheuvel
2023-01-13 23:25           ` Ard Biesheuvel
2023-01-14 11:24           ` Sedat Dilek
2023-01-14 11:24             ` Sedat Dilek
2023-01-14 11:24             ` Sedat Dilek
2023-01-14 11:28             ` Sedat Dilek
2023-01-14 11:28               ` Sedat Dilek
2023-01-14 11:28               ` Sedat Dilek
2023-01-15  0:27               ` Matthew Wilcox
2023-01-15  0:27                 ` Matthew Wilcox
2023-01-15  0:27                 ` Matthew Wilcox
2023-01-15 12:04                 ` Sedat Dilek
2023-01-15 12:04                   ` Sedat Dilek
2023-01-15 12:04                   ` Sedat Dilek
2023-01-16  9:42                   ` John Paul Adrian Glaubitz
2023-01-16  9:42                     ` John Paul Adrian Glaubitz
2023-01-16  9:42                     ` John Paul Adrian Glaubitz
2023-01-16  9:41                 ` John Paul Adrian Glaubitz
2023-01-16  9:41                   ` John Paul Adrian Glaubitz
2023-01-16  9:41                   ` John Paul Adrian Glaubitz
2023-01-16 13:28                   ` Matthew Wilcox
2023-01-16 13:28                     ` Matthew Wilcox
2023-01-16 13:28                     ` Matthew Wilcox
2023-01-16  9:40               ` John Paul Adrian Glaubitz
2023-01-16  9:40                 ` John Paul Adrian Glaubitz
2023-01-16  9:40                 ` John Paul Adrian Glaubitz
2023-01-16  9:37             ` John Paul Adrian Glaubitz
2023-01-16  9:37               ` John Paul Adrian Glaubitz
2023-01-16  9:37               ` John Paul Adrian Glaubitz
2023-01-16  9:32           ` John Paul Adrian Glaubitz
2023-01-16  9:32             ` John Paul Adrian Glaubitz
2023-01-16  9:32             ` John Paul Adrian Glaubitz
2023-01-16 10:09             ` Ard Biesheuvel
2023-01-16 10:09               ` Ard Biesheuvel
2023-01-16 10:09               ` Ard Biesheuvel
2023-01-13  1:12   ` lockref scalability on x86-64 vs cpu_relax Mateusz Guzik
2023-01-13  1:12     ` Mateusz Guzik
2023-01-13  1:12     ` Mateusz Guzik
2023-01-13  4:08     ` Linus Torvalds
2023-01-13  4:08       ` Linus Torvalds
2023-01-13  4:08       ` Linus Torvalds
2023-01-13  9:46     ` Will Deacon
2023-01-13  9:46       ` Will Deacon
2023-01-13  9:46       ` Will Deacon
2023-01-13  3:20   ` Nicholas Piggin
2023-01-13  3:20     ` Nicholas Piggin
2023-01-13  3:20     ` Nicholas Piggin
2023-01-13  4:15     ` Linus Torvalds
2023-01-13  4:15       ` Linus Torvalds
2023-01-13  4:15       ` Linus Torvalds
2023-01-13  5:36       ` Nicholas Piggin
2023-01-13  5:36         ` Nicholas Piggin
2023-01-13  5:36         ` Nicholas Piggin
2023-01-16 14:08     ` Memory transaction instructions David Howells
2023-01-16 14:08       ` David Howells
2023-01-16 15:09       ` Matthew Wilcox
2023-01-16 15:09         ` Matthew Wilcox
2023-01-16 15:09         ` Matthew Wilcox
2023-01-16 16:59       ` Linus Torvalds
2023-01-16 16:59         ` Linus Torvalds
2023-01-16 16:59         ` Linus Torvalds
2023-01-18  9:05       ` David Howells
2023-01-18  9:05         ` David Howells
2023-01-18  9:05         ` David Howells
2023-01-19  1:41         ` Nicholas Piggin
2023-01-19  1:41           ` Nicholas Piggin
2023-01-19  1:41           ` Nicholas Piggin
2023-01-13 10:23   ` lockref scalability on x86-64 vs cpu_relax Peter Zijlstra
2023-01-13 10:23     ` Peter Zijlstra
2023-01-13 10:23     ` Peter Zijlstra
2023-01-13 18:44   ` [PATCH] lockref: stop doing cpu_relax in the cmpxchg loop Mateusz Guzik
2023-01-13 18:44     ` Mateusz Guzik
2023-01-13 18:44     ` Mateusz Guzik
2023-01-13 21:47     ` Luck, Tony [this message]
2023-01-13 21:47       ` Luck, Tony
2023-01-13 21:47       ` Luck, Tony
2023-01-13 23:31       ` Linus Torvalds
2023-01-13 23:31         ` Linus Torvalds
2023-01-13 23:31         ` Linus Torvalds

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