From: David Howells <dhowells@redhat.com>
To: John Hubbard <jhubbard@nvidia.com>
Cc: dhowells@redhat.com, Al Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
Jens Axboe <axboe@kernel.dk>, "Jan Kara" <jack@suse.cz>,
Jeff Layton <jlayton@kernel.org>,
David Hildenbrand <david@redhat.com>,
Jason Gunthorpe <jgg@nvidia.com>,
Logan Gunthorpe <logang@deltatee.com>,
linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, "Christoph Hellwig" <hch@lst.de>
Subject: Re: [PATCH v9 4/8] block: Fix bio_flagged() so that gcc can better optimise it
Date: Tue, 24 Jan 2023 20:55:11 +0000 [thread overview]
Message-ID: <1297525.1674593711@warthog.procyon.org.uk> (raw)
In-Reply-To: <ad671496-2461-0b25-48c8-bf474fffe41d@nvidia.com>
John Hubbard <jhubbard@nvidia.com> wrote:
> I don't know how you noticed that this was even a problem! Neatly
> fixed.
I wanted BIO_PAGE_REFFED/PINNED to translate to FOLL_GET/PIN with no more than
a single AND instruction, assuming they were assigned to the same values (1 &
2), so I checked to see what assembly was produced by:
gup_flags |= bio_flagged(bio, BIO_PAGE_REFFED) ? FOLL_GET : 0;
gup_flags |= bio_flagged(bio, BIO_PAGE_PINNED) ? FOLL_PIN : 0;
Complicated though it looks, it should optimise down to something like:
and $3,%eax
assuming something like REFFED/GET == 0x1 and PINNED/PIN == 0x2.
David
next prev parent reply other threads:[~2023-01-24 20:56 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-24 17:01 [PATCH v9 0/8] iov_iter: Improve page extraction (pin or just list) David Howells
2023-01-24 17:01 ` [PATCH v9 1/8] iov_iter: Define flags to qualify page extraction David Howells
2023-01-24 19:00 ` Christoph Hellwig
2023-01-24 19:23 ` John Hubbard
2023-01-24 17:01 ` [PATCH v9 2/8] iov_iter: Add a function to extract a page list from an iterator David Howells
2023-01-24 19:00 ` Christoph Hellwig
2023-01-24 20:50 ` John Hubbard
2023-01-24 21:10 ` David Howells
2023-01-24 17:01 ` [PATCH v9 3/8] iomap: Don't get an reference on ZERO_PAGE for direct I/O block zeroing David Howells
2023-01-24 19:01 ` Christoph Hellwig
2023-01-24 20:41 ` David Howells
2023-01-25 6:28 ` Christoph Hellwig
2023-01-24 19:25 ` John Hubbard
2023-01-24 17:01 ` [PATCH v9 4/8] block: Fix bio_flagged() so that gcc can better optimise it David Howells
2023-01-24 19:28 ` John Hubbard
2023-01-24 20:55 ` David Howells [this message]
2023-01-24 17:01 ` [PATCH v9 5/8] block: Replace BIO_NO_PAGE_REF with BIO_PAGE_REFFED with inverted logic David Howells
2023-01-24 19:01 ` Christoph Hellwig
2023-01-24 19:47 ` John Hubbard
2023-01-24 21:17 ` David Howells
2023-01-25 6:30 ` Christoph Hellwig
2023-01-24 17:01 ` [PATCH v9 6/8] block: Switch to pinning pages David Howells
2023-01-24 19:02 ` Christoph Hellwig
2023-01-24 20:59 ` David Howells
2023-01-25 6:30 ` Christoph Hellwig
2023-01-24 19:50 ` John Hubbard
2023-01-24 17:01 ` [PATCH v9 7/8] block: Convert bio_iov_iter_get_pages to use iov_iter_extract_pages David Howells
2023-01-24 19:03 ` Christoph Hellwig
2023-01-24 20:00 ` John Hubbard
2023-01-24 20:46 ` David Howells
2023-01-24 17:01 ` [PATCH v9 8/8] block: convert bio_map_user_iov " David Howells
2023-01-24 19:03 ` Christoph Hellwig
2023-01-24 20:08 ` John Hubbard
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