From: Catalin Marinas <catalin.marinas@arm.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Justin Stitt <justinstitt@google.com>,
Jakub Kicinski <kuba@kernel.org>,
Leon Romanovsky <leon@kernel.org>,
linux-rdma@vger.kernel.org, linux-s390@vger.kernel.org,
llvm@lists.linux.dev, Ingo Molnar <mingo@redhat.com>,
Bill Wendling <morbo@google.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
netdev@vger.kernel.org, Paolo Abeni <pabeni@redhat.com>,
Salil Mehta <salil.mehta@huawei.com>,
Jijie Shao <shaojijie@huawei.com>,
Sven Schnelle <svens@linux.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
x86@kernel.org, Yisen Zhuang <yisen.zhuang@huawei.com>,
Arnd Bergmann <arnd@arndb.de>,
Leon Romanovsky <leonro@mellanox.com>,
linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
Mark Rutland <mark.rutland@arm.com>,
Michael Guralnik <michaelgur@mellanox.com>,
patches@lists.linux.dev, Niklas Schnelle <schnelle@linux.ibm.com>,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH 4/6] arm64/io: Provide a WC friendly __iowriteXX_copy()
Date: Thu, 29 Feb 2024 10:24:42 +0000 [thread overview]
Message-ID: <ZeBbamDoHIxzzfof@arm.com> (raw)
In-Reply-To: <20240228230616.GS13330@nvidia.com>
On Wed, Feb 28, 2024 at 07:06:16PM -0400, Jason Gunthorpe wrote:
> On Tue, Feb 27, 2024 at 10:37:18AM +0000, Catalin Marinas wrote:
> > On Tue, Feb 20, 2024 at 09:17:08PM -0400, Jason Gunthorpe wrote:
> > > +/*
> > > + * This generates a memcpy that works on a from/to address which is aligned to
> > > + * bits. Count is in terms of the number of bits sized quantities to copy. It
> > > + * optimizes to use the STR groupings when possible so that it is WC friendly.
> > > + */
> > > +#define memcpy_toio_aligned(to, from, count, bits) \
> > > + ({ \
> > > + volatile u##bits __iomem *_to = to; \
> > > + const u##bits *_from = from; \
> > > + size_t _count = count; \
> > > + const u##bits *_end_from = _from + ALIGN_DOWN(_count, 8); \
> > > + \
> > > + for (; _from < _end_from; _from += 8, _to += 8) \
> > > + __const_memcpy_toio_aligned##bits(_to, _from, 8); \
> > > + if ((_count % 8) >= 4) { \
> > > + __const_memcpy_toio_aligned##bits(_to, _from, 4); \
> > > + _from += 4; \
> > > + _to += 4; \
> > > + } \
> > > + if ((_count % 4) >= 2) { \
> > > + __const_memcpy_toio_aligned##bits(_to, _from, 2); \
> > > + _from += 2; \
> > > + _to += 2; \
> > > + } \
> > > + if (_count % 2) \
> > > + __const_memcpy_toio_aligned##bits(_to, _from, 1); \
> > > + })
> >
> > Do we actually need all this if count is not constant? If it's not
> > performance critical anywhere, I'd rather copy the generic
> > implementation, it's easier to read.
>
> Which generic version?
The current __iowriteXX_copy() in lib/iomap_copy.c (copy them over or
add some preprocessor reuse the generic functions).
> The point is to maximize WC effects with non-constant values, so I
> think we do need something like this. ie we can't just fall back to
> looping over 64 bit stores one at a time.
If that's a case you are also targeting and have seen it in practice,
that's fine. But I had the impression that you are mostly after the
constant count case which is already addressed by the other part of this
patch. For the non-constant case, we have a DGH only at the end of
whatever buffer was copied rather than after every 64-byte increments
you'd get for a count of 8.
> Most places I know about using this are performance paths, the entire
> iocopy infrastructure was introduced as an x86 performance
> optimization..
At least the x86 case makes sense even from a maintenance perspective,
it's just a much simpler "rep movsl". I just want to make sure we don't
over-complicate this code on arm64 unnecessarily.
--
Catalin
next prev parent reply other threads:[~2024-02-29 10:24 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-21 1:17 [PATCH 0/6] Fix mlx5 write combining support on new ARM64 cores Jason Gunthorpe
2024-02-21 1:17 ` [PATCH 1/6] x86: Stop using weak symbols for __iowrite32_copy() Jason Gunthorpe
2024-02-21 1:17 ` [PATCH 2/6] s390: Implement __iowrite32_copy() Jason Gunthorpe
2024-02-21 1:17 ` [PATCH 3/6] s390: Stop using weak symbols for __iowrite64_copy() Jason Gunthorpe
2024-02-21 1:17 ` [PATCH 4/6] arm64/io: Provide a WC friendly __iowriteXX_copy() Jason Gunthorpe
2024-02-21 19:22 ` Will Deacon
2024-02-21 23:28 ` Jason Gunthorpe
2024-02-22 22:05 ` David Laight
2024-02-22 22:36 ` Jason Gunthorpe
2024-02-23 9:07 ` David Laight
2024-02-23 11:01 ` Niklas Schnelle
2024-02-23 11:05 ` David Laight
2024-02-23 12:53 ` Jason Gunthorpe
2024-02-23 11:38 ` Niklas Schnelle
2024-02-23 12:19 ` David Laight
2024-02-23 13:03 ` Jason Gunthorpe
2024-02-23 13:52 ` David Laight
2024-02-23 14:44 ` Jason Gunthorpe
2024-02-23 12:58 ` Jason Gunthorpe
2024-02-23 16:35 ` Niklas Schnelle
2024-02-23 17:05 ` Jason Gunthorpe
2024-02-27 10:37 ` Catalin Marinas
2024-02-28 23:06 ` Jason Gunthorpe
2024-02-29 10:24 ` Catalin Marinas [this message]
2024-02-29 13:28 ` Jason Gunthorpe
2024-02-29 10:33 ` Catalin Marinas
2024-02-29 13:29 ` Jason Gunthorpe
2024-03-01 18:52 ` Catalin Marinas
2024-02-21 1:17 ` [PATCH 5/6] net: hns3: Remove io_stop_wc() calls after __iowrite64_copy() Jason Gunthorpe
2024-02-22 0:57 ` Jijie Shao
2024-02-21 1:17 ` [PATCH 6/6] IB/mlx5: Use __iowrite64_copy() for write combining stores Jason Gunthorpe
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