From: Jisheng Zhang <jszhang@kernel.org>
To: Conor Dooley <conor@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>, Guo Ren <guoren@kernel.org>,
linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 0/2] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO
Date: Thu, 12 Oct 2023 22:40:46 +0800 [thread overview]
Message-ID: <ZSgFbuD203L0XL4J@xhacker> (raw)
In-Reply-To: <20231012-remindful-coke-f9cfe950425f@spud>
On Thu, Oct 12, 2023 at 03:36:28PM +0100, Conor Dooley wrote:
> On Thu, Oct 12, 2023 at 10:21:08PM +0800, Jisheng Zhang wrote:
> > On Thu, Oct 12, 2023 at 10:14:54PM +0800, Jisheng Zhang wrote:
> > > Previously, we use alternative mechanism to dynamically patch
> > > the CMO operations for THEAD C906/C910 during boot for performance
> > > reason. But as pointed out by Arnd, "there is already a significant
> > > cost in accessing the invalidated cache lines afterwards, which is
> > > likely going to be much higher than the cost of an indirect branch".
> > > And indeed, there's no performance difference with GMAC and EMMC per
> > > my test on Sipeed Lichee Pi 4A board.
> > >
> > > Use riscv_nonstd_cache_ops for THEAD C906/C910 CMO to simplify
> > > the alternative code, and to acchieve Arnd's goal -- "I think
> > > moving the THEAD ops at the same level as all nonstandard operations
> > > makes sense, but I'd still leave CMO as an explicit fast path that
> > > avoids the indirect branch. This seems like the right thing to do both
> > > for readability and for platforms on which the indirect branch has a
> > > noticeable overhead."
> > >
> > > To make bisect easy, I use two patches here: patch1 does the conversion
> > > which just mimics current CMO behavior via. riscv_nonstd_cache_ops, I
> > > assume no functionalities changes. patch2 uses T-HEAD PA based CMO
> > > instructions so that we don't need to covert PA to VA.
> > >
> > > Hi Guo,
> > >
> > > I didn't use wback_inv for wback as you suggested during v1 reviewing,
> > > this can be left as future optimizations.
> > >
> > > Thanks
> > >
> > > since v2:
> > > - collect Reviewed-by tag
> >
> > Oh, I missed the tag collection, but I know maintainers are using b4 which can
> > collect and apply tags automatically ;). let me know if want a new
> > version.
>
> It doesn't collect tags (AFAIU) from earlier revisions though.
oops I didn't know this before, just sent out v4 with real tag collection to
make the merging progress smooth.
prev parent reply other threads:[~2023-10-12 14:53 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-12 14:14 [PATCH v3 0/2] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO Jisheng Zhang
2023-10-12 14:14 ` [PATCH v3 1/2] " Jisheng Zhang
2023-10-12 14:36 ` Conor Dooley
2023-10-12 14:14 ` [PATCH v3 2/2] riscv: errata: thead: use pa based instructions " Jisheng Zhang
2023-10-12 14:21 ` [PATCH v3 0/2] riscv: errata: thead: use riscv_nonstd_cache_ops " Jisheng Zhang
2023-10-12 14:36 ` Conor Dooley
2023-10-12 14:40 ` Jisheng Zhang [this message]
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=ZSgFbuD203L0XL4J@xhacker \
--to=jszhang@kernel.org \
--cc=aou@eecs.berkeley.edu \
--cc=conor@kernel.org \
--cc=guoren@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-riscv@lists.infradead.org \
--cc=palmer@dabbelt.com \
--cc=paul.walmsley@sifive.com \
/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