From: "Lluís Vilanova" <vilanova@ac.upc.edu>
To: "Emilio G. Cota" <cota@braap.org>
Cc: "QEMU Developers" <qemu-devel@nongnu.org>,
"MTTCG Devel" <mttcg@greensocs.com>,
"Alex Bennée" <alex.bennee@linaro.org>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Richard Henderson" <rth@twiddle.net>,
"Sergey Fedorov" <serge.fdrv@gmail.com>,
"Alvise Rigo" <a.rigo@virtualopensystems.com>,
"Peter Maydell" <peter.maydell@linaro.org>
Subject: Re: [Qemu-devel] [RFC 00/30] cmpxchg-based emulation of atomics
Date: Tue, 28 Jun 2016 10:45:28 +0200 [thread overview]
Message-ID: <874m8dem6v.fsf@fimbulvetr.bsc.es> (raw)
In-Reply-To: <1467054136-10430-1-git-send-email-cota@braap.org> (Emilio G. Cota's message of "Mon, 27 Jun 2016 15:01:46 -0400")
Emilio G Cota writes:
[...]
> - What to do when atomic ops are used on something other than RAM?
> Should we have a "slow path" that is not atomic for these cases, or
> it's OK to assume code is bogus? For now, I just wrote XXX.
[...]
You mean, for example, on I/O space? In these cases, it depends on the specific
device you're accessing and the interconnect used to access it.
TL;DR: In some cases, it makes sense to support atomics outside RAM.
For example, PCIe has support for expressing atomic operations in its messages
(I'm sure other interconnects do too). But in the end it depends on whether the
device supports them (I'm not sure if the device can reject atomics and produce
an error to whomever tried to do the atomic access, or if they are simply
ignored).
Cheers,
Lluis
next prev parent reply other threads:[~2016-06-28 8:45 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-27 19:01 [Qemu-devel] [RFC 00/30] cmpxchg-based emulation of atomics Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 01/30] softmmu: add cmpxchg helpers Emilio G. Cota
2016-06-27 20:11 ` Richard Henderson
2016-06-27 21:19 ` Emilio G. Cota
2016-06-27 21:43 ` Richard Henderson
2016-06-27 21:48 ` Peter Maydell
2016-06-27 21:53 ` Richard Henderson
2016-06-27 19:01 ` [Qemu-devel] [RFC 02/30] tcg: add tcg_cmpxchg_lock Emilio G. Cota
2016-06-27 20:07 ` Richard Henderson
2016-06-27 20:41 ` Emilio G. Cota
2016-06-27 21:02 ` Richard Henderson
2016-06-27 19:01 ` [Qemu-devel] [RFC 03/30] cpu_ldst: add cpu_cmpxchg helpers Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 04/30] target-i386: add cmpxchg helpers Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 05/30] target-i386: emulate LOCK'ed cmpxchg using " Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 06/30] target-i386: emulate LOCK'ed cmpxchg8b/16b " Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 07/30] atomics: add atomic_xor Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 08/30] atomics: add atomic_op_fetch variants Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 09/30] softmmu: add atomic helpers Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 10/30] cpu_ldst: add cpu_atomic helpers Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 11/30] target-i386: add atomic helpers Emilio G. Cota
2016-06-27 20:27 ` Richard Henderson
2016-06-27 21:39 ` Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 12/30] target-i386: emulate LOCK'ed OP instructions using " Emilio G. Cota
2016-06-27 19:01 ` [Qemu-devel] [RFC 13/30] target-i386: emulate LOCK'ed INC using atomic helper Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 14/30] target-i386: emulate LOCK'ed NOT " Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 15/30] target-i386: emulate LOCK'ed NEG using cmpxchg helper Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 16/30] target-i386: emulate LOCK'ed XADD using atomic helper Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 17/30] target-i386: emulate LOCK'ed BTX ops using atomic helpers Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 18/30] target-i386: emulate XCHG using atomic helper Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 19/30] tests: add atomic_add-bench Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 20/30] target-i386: remove helper_lock() Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 21/30] target-arm: add cmpxchg helpers Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 22/30] target-arm: emulate LL/SC using " Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 23/30] target-arm: add atomic_xchg helper Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 24/30] target-arm: emulate SWP with " Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 25/30] helper: add DEF_HELPER_6 Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 26/30] target-arm: add cmpxchg helpers for aarch64 Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 27/30] target-arm: emulate aarch64's LL/SC using cmpxchg helpers Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 28/30] linux-user: remove handling of ARM's EXCP_STREX Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 29/30] linux-user: remove handling of aarch64's EXCP_STREX Emilio G. Cota
2016-06-27 19:02 ` [Qemu-devel] [RFC 30/30] target-arm: remove EXCP_STREX + cpu_exclusive_{test, info} Emilio G. Cota
2016-06-28 8:45 ` Lluís Vilanova [this message]
2016-06-28 15:48 ` [Qemu-devel] [RFC 00/30] cmpxchg-based emulation of atomics Richard Henderson
2016-06-28 19:52 ` Emilio G. Cota
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