From: Andrew Cooper <andrew.cooper3@citrix.com>
To: torvalds@linux-foundation.org
Cc: alex@ghiti.fr, aou@eecs.berkeley.edu, axboe@kernel.dk,
bp@alien8.de, brauner@kernel.org, catalin.marinas@arm.com,
christophe.leroy@csgroup.eu, dave.hansen@intel.com,
dave.hansen@linux.intel.com, david.laight.linux@gmail.com,
edumazet@google.com, hpa@zytor.com, kuni1840@gmail.com,
kuniyu@google.com, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
linuxppc-dev@lists.ozlabs.org, maddy@linux.ibm.com,
mingo@redhat.com, mpe@ellerman.id.au, npiggin@gmail.com,
palmer@dabbelt.com, pjw@kernel.org, tglx@linutronix.de,
will@kernel.org, x86@kernel.org
Subject: Re: [PATCH v1 2/2] epoll: Use __user_write_access_begin() and unsafe_put_user() in epoll_put_uevent().
Date: Wed, 29 Oct 2025 01:42:42 +0000 [thread overview]
Message-ID: <5bc35f89-1b77-4c0c-b6ea-fe9b2cb74870@citrix.com> (raw)
In-Reply-To: <CAHk-=wiTN=1Sm5DVnXDtQ-tSiPuz-7QVpgP2vt6LgaEnhbubfw@mail.gmail.com>
> Yeah, clac/stac are horrenously expensive on Zen 2. I think they are
> microcoded - and not the fast kind - so effectively serializing.
AIUI, Zen5 is the first uarch capable of renaming the AC flag.
This make STAC/CLAC "lfence-like" in practice on older CPUs, because of
an implementation constraint of not being able to execute speculatively.
~Andrew
next prev parent reply other threads:[~2025-10-29 1:42 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-23 0:04 [PATCH v1 0/2] epoll: Save one stac/clac pair " Kuniyuki Iwashima
2025-10-23 0:04 ` [PATCH v1 1/2] uaccess: Add __user_write_access_begin() Kuniyuki Iwashima
2025-10-23 5:37 ` Linus Torvalds
2025-10-23 8:29 ` David Laight
2025-10-24 5:31 ` Kuniyuki Iwashima
2025-10-23 0:04 ` [PATCH v1 2/2] epoll: Use __user_write_access_begin() and unsafe_put_user() in epoll_put_uevent() Kuniyuki Iwashima
2025-10-23 19:40 ` Dave Hansen
2025-10-24 5:16 ` Kuniyuki Iwashima
2025-10-24 14:05 ` Dave Hansen
2025-10-24 14:47 ` David Laight
2025-10-28 5:32 ` Kuniyuki Iwashima
2025-10-28 9:54 ` David Laight
2025-10-28 16:42 ` Kuniyuki Iwashima
2025-10-28 16:58 ` Linus Torvalds
2025-10-29 1:42 ` Andrew Cooper [this message]
2025-10-28 22:30 ` David Laight
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