linux-kernel - Re: [PATCH 01/29] iov_iter: Switch to using a table of operations

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Message-ID: <254318.1606051984@warthog.procyon.org.uk>
Date:   Sun, 22 Nov 2020 13:33:04 +0000
From:   David Howells <dhowells@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     dhowells@...hat.com, Pavel Begunkov <asml.silence@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/29] iov_iter: Switch to using a table of operations

Linus Torvalds <torvalds@...ux-foundation.org> wrote:

>  - I worry a bit about the indirect call overhead and spectre v2.

I don't know enough about how spectre v2 works to say if this would be a
problem for the ops-table approach, but wouldn't it also affect the chain of
conditional branches that we currently use, since it's branch-prediction
based?

David