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From: Paul Walmsley <paul.walmsley@sifive.com>
To: Christopher Lameter <cl@linux.com>
Cc: "Nick Kossifidis" <mick@ics.forth.gr>,
	"Björn Töpel" <bjorn.topel@gmail.com>,
	"Paul Walmsley" <paul@pwsan.com>,
	"Palmer Dabbelt" <palmer@sifive.com>,
	linux-riscv@lists.infradead.org
Subject: Re: per-cpu thoughts
Date: Thu, 28 Feb 2019 04:20:23 -0800 (PST)	[thread overview]
Message-ID: <alpine.DEB.2.21.9999.1902280418110.10847@viisi.sifive.com> (raw)
In-Reply-To: <0100016916c7cda0-9622bc7c-b8db-4967-83e6-43692aa58ec8-000000@email.amazonses.com>

[-- Attachment #1: Type: text/plain, Size: 793 bytes --]

On Fri, 22 Feb 2019, Christopher Lameter wrote:

> On Fri, 22 Feb 2019, Björn Töpel wrote:
> 
> > > The problem is that the register needs to be referenced by the amo
> > > instruction. Can amoadd increment an address relative to a scratch
> > > register?
> > >
> >
> > It cannot. So, we'll end up with (at least) a preempt disabled region...
> 
> If we need to do that then we already have so much overhead due to that
> processing that it may not be worthwhile. lc/sc overhead is minor compared
> to switching preempt on and off I think.

Is it strictly necessary to disable and re-enable preemption?  

On a UMA system, it might be preferable to risk the cost of the cache line 
bounce than to flip preemption off and on - assuming there's no other 
impact.


- Paul

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  reply	other threads:[~2019-02-28 12:20 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-20 19:57 per-cpu thoughts Björn Töpel
2019-02-21 15:57 ` Christopher Lameter
2019-02-21 16:28 ` Paul Walmsley
2019-02-21 17:24   ` Björn Töpel
2019-02-21 17:49     ` Paul Walmsley
2019-02-21 19:40       ` Palmer Dabbelt
2019-02-22 15:04         ` Christopher Lameter
2019-02-22 15:36           ` Nick Kossifidis
2019-02-22 15:56             ` Christopher Lameter
2019-02-22 19:47               ` Björn Töpel
2019-02-22 19:56                 ` Christopher Lameter
2019-02-28 12:20                   ` Paul Walmsley [this message]
2019-02-28 17:58                     ` Christopher Lameter
2019-02-28 18:42                       ` Paul Walmsley
2019-02-28 19:09                         ` Christopher Lameter
2019-02-28 20:21                           ` Paul Walmsley
2019-03-01  1:13                             ` Christopher Lameter
2019-03-08  7:17                   ` Björn Töpel
2019-03-11 13:22                     ` Palmer Dabbelt
2019-03-11 14:48                       ` Björn Töpel
2019-03-11 14:56                         ` Christopher Lameter
2019-03-11 15:05                           ` Björn Töpel
2019-03-11 15:26                             ` Paul Walmsley
2019-03-11 16:48                               ` Mark Rutland
2019-03-11 18:39                                 ` Paul Walmsley
2019-03-12 11:23                                   ` Mark Rutland
2019-03-12 16:01                                     ` Paul Walmsley
2019-03-12 17:34                                       ` Christopher Lameter
2019-03-12  4:26                               ` Christopher Lameter
2019-03-12 14:21                                 ` Paul Walmsley
2019-03-12 17:42                                   ` Christopher Lameter
2019-03-12 17:59                                     ` Gary Guo
2019-03-13 18:58                                       ` Christopher Lameter
2019-03-13 20:15                                     ` Paul Walmsley
2019-03-22 14:51                               ` Nick Kossifidis
2019-03-22 17:57                                 ` Christopher Lameter
2019-03-11 15:51                             ` Christopher Lameter
2019-03-11 16:35                               ` Björn Töpel
2019-03-12  4:22                                 ` Christopher Lameter
2019-02-22 19:48             ` Björn Töpel
2019-02-22 20:53               ` Nick Kossifidis

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