From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>, Borislav Petkov <bpetkov@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Nadav Amit <nadav.amit@gmail.com>, Rik van Riel <riel@redhat.com>
Subject: Re: [RFC 01/11] x86/ldt: Simplify LDT switching logic
Date: Mon, 5 Jun 2017 15:51:52 -0700 [thread overview]
Message-ID: <CA+55aFwo5UXidsA23FcbD6+VCSbWC9ZHt65it9q9f0L_hycPLw@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFwrCep+F8zV-fK5ufiDRX+N9yTcHMsyR-JhvFeoD-1LYg@mail.gmail.com>
On Mon, Jun 5, 2017 at 3:40 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> I think the "LDT didn't match" was really just a simpler and more
> efficient way to say "they weren't both NULL".
In fact, looking back in the history, it used to instead add the sizes
of the context (and then similar logic: "if the sum is non-zero, one
or the other was non-zero").
Commit 0bbed3beb4 ("[PATCH] Thread-Local Storage (TLS) support") in
the historical tree then did this:
- if (next->context.size+prev->context.size)
+ if (unlikely(prev->context.ldt != next->context.ldt))
I'm ok with your change, but I reacted to the commit log about how
this was "overcomplicated". It was actually an optimization exactly to
avoid two compares..
Linus
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next prev parent reply other threads:[~2017-06-05 22:51 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-05 22:36 [RFC 00/11] PCID and improved laziness Andy Lutomirski
2017-06-05 22:36 ` [RFC 01/11] x86/ldt: Simplify LDT switching logic Andy Lutomirski
2017-06-05 22:40 ` Linus Torvalds
2017-06-05 22:44 ` Andy Lutomirski
2017-06-05 22:51 ` Linus Torvalds [this message]
2017-06-05 22:36 ` [RFC 02/11] x86/mm: Remove reset_lazy_tlbstate() Andy Lutomirski
2017-06-05 22:36 ` [RFC 03/11] x86/mm: Give each mm TLB flush generation a unique ID Andy Lutomirski
2017-06-05 22:36 ` [RFC 04/11] x86/mm: Track the TLB's tlb_gen and update the flushing algorithm Andy Lutomirski
2017-06-06 5:03 ` Nadav Amit
2017-06-06 22:45 ` Andy Lutomirski
2017-06-05 22:36 ` [RFC 05/11] x86/mm: Rework lazy TLB mode and TLB freshness tracking Andy Lutomirski
2017-06-06 1:39 ` Nadav Amit
2017-06-06 21:23 ` Andy Lutomirski
2017-06-06 19:11 ` Rik van Riel
2017-06-06 21:34 ` Andy Lutomirski
2017-06-07 3:33 ` Rik van Riel
2017-06-07 4:54 ` Andy Lutomirski
2017-06-07 5:11 ` Andy Lutomirski
2017-06-05 22:36 ` [RFC 06/11] x86/mm: Stop calling leave_mm() in idle code Andy Lutomirski
2017-06-05 22:36 ` [RFC 07/11] x86/mm: Disable PCID on 32-bit kernels Andy Lutomirski
2017-06-05 22:36 ` [RFC 08/11] x86/mm: Add nopcid to turn off PCID Andy Lutomirski
2017-06-06 3:22 ` Andi Kleen
2017-06-14 4:52 ` Andy Lutomirski
2017-06-14 9:51 ` Borislav Petkov
2017-06-05 22:36 ` [RFC 09/11] x86/mm: Teach CR3 readers about PCID Andy Lutomirski
2017-06-05 22:36 ` [RFC 10/11] x86/mm: Enable CR4.PCIDE on supported systems Andy Lutomirski
2017-06-06 21:31 ` Boris Ostrovsky
2017-06-06 21:35 ` Andy Lutomirski
2017-06-06 21:48 ` Boris Ostrovsky
2017-06-06 21:54 ` Andy Lutomirski
2017-06-05 22:36 ` [RFC 11/11] x86/mm: Try to preserve old TLB entries using PCID Andy Lutomirski
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