All of lore.kernel.org
 help / color / mirror / Atom feed
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.

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

WARNING: multiple messages have this Message-ID (diff)
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.

  reply	other threads:[~2023-10-12 14:53 UTC|newest]

Thread overview: 14+ 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 ` Jisheng Zhang
2023-10-12 14:14 ` [PATCH v3 1/2] " Jisheng Zhang
2023-10-12 14:14   ` Jisheng Zhang
2023-10-12 14:36   ` Conor Dooley
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 14:14   ` Jisheng Zhang
2023-10-12 14:21 ` [PATCH v3 0/2] riscv: errata: thead: use riscv_nonstd_cache_ops " Jisheng Zhang
2023-10-12 14:21   ` Jisheng Zhang
2023-10-12 14:36   ` Conor Dooley
2023-10-12 14:36     ` Conor Dooley
2023-10-12 14:40     ` Jisheng Zhang [this message]
2023-10-12 14:40       ` Jisheng Zhang

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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.