From: Zachary Amsden <zach@vmware.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Chris Wright <chrisw@sous-sol.org>,
Virtualization Mailing List <virtualization@lists.osdl.org>
Subject: Re: RFC: const_udelay in 018-delay functions patch
Date: Tue, 24 Oct 2006 23:21:50 -0700 [thread overview]
Message-ID: <453F027E.2020704@vmware.com> (raw)
In-Reply-To: <1161756217.15099.52.camel@localhost.localdomain>
Rusty Russell wrote:
> On Tue, 2006-10-24 at 22:11 -0700, Zachary Amsden wrote:
>
>> So I implemented udelay and ndelay through a single paravirt_op,
>> const_udelay, instead of having either two separate paravirt-ops for
>> udelay or ndelay, or a redundant const_udelay paravirt_op. Anybody have
>> any objection to reworking the patch this way?
>>
>
> Seems saner, but I'm not sure why x86 has an I/O delay separate from
> udelay to start with?
>
I/O delay is for slow hardware that needs a couple bus cycles to settle,
but doesn't have specified latency requirements - like many old floppy
drive controllers. Using the jmp 1f; thing doesn't seem very future
proof, and the port I/O guarantees a bus access, which makes these
fuggly older controllers work better.
> Comments:
>
>
>> +#if defined(CONFIG_PARAVIRT) && !defined(USE_REAL_IO)
>> +#include <asm/paravirt.h>
>> +#else
>>
>
> USE_REAL_IO? Is this defined anywhere? Or just future-proofing?
>
It has to be used for SMP bootstrapping - IPI acceptance requires real
time cross-processor delay, even in a VM - and also can be added by a
top-level define to kernel compiles for driver domains for Xen to give
real time device delays.
Zach
next prev parent reply other threads:[~2006-10-25 6:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-10-25 5:11 RFC: const_udelay in 018-delay functions patch Zachary Amsden
2006-10-25 6:03 ` Rusty Russell
2006-10-25 6:21 ` Zachary Amsden [this message]
2006-10-25 23:01 ` Rusty Russell
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=453F027E.2020704@vmware.com \
--to=zach@vmware.com \
--cc=chrisw@sous-sol.org \
--cc=rusty@rustcorp.com.au \
--cc=virtualization@lists.osdl.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).