From: Qian Cai <cai@lca.pw>
To: Paul Mackerras <paulus@ozlabs.org>
Cc: mpe@ellerman.id.au, benh@kernel.crashing.org, aik@ozlabs.ru,
paulmck@kernel.org, linuxppc-dev@lists.ozlabs.org,
kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc/kvm/book3s64/vio: fix some RCU-list locks
Date: Tue, 26 May 2020 21:22:45 -0400 [thread overview]
Message-ID: <20200527012245.GJ991@lca.pw> (raw)
In-Reply-To: <20200527011323.GA293451@thinks.paulus.ozlabs.org>
On Wed, May 27, 2020 at 11:13:23AM +1000, Paul Mackerras wrote:
> On Sun, May 10, 2020 at 01:18:34AM -0400, Qian Cai wrote:
> > It is unsafe to traverse kvm->arch.spapr_tce_tables and
> > stt->iommu_tables without the RCU read lock held. Also, add
> > cond_resched_rcu() in places with the RCU read lock held that could take
> > a while to finish.
>
> This mostly looks fine. The cond_resched_rcu() in kvmppc_tce_validate
> doesn't seem necessary (the list would rarely have more than a few
> dozen entries) and could be a performance problem given that TCE
> validation is a hot-path.
>
> Are you OK with me modifying the patch to take out that
> cond_resched_rcu(), or is there some reason why it's essential that it
> be there?
Feel free to take out that cond_resched_rcu(). Your reasoning makes
sense.
WARNING: multiple messages have this Message-ID (diff)
From: Qian Cai <cai@lca.pw>
To: Paul Mackerras <paulus@ozlabs.org>
Cc: paulmck@kernel.org, aik@ozlabs.ru, linux-kernel@vger.kernel.org,
kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc/kvm/book3s64/vio: fix some RCU-list locks
Date: Tue, 26 May 2020 21:22:45 -0400 [thread overview]
Message-ID: <20200527012245.GJ991@lca.pw> (raw)
In-Reply-To: <20200527011323.GA293451@thinks.paulus.ozlabs.org>
On Wed, May 27, 2020 at 11:13:23AM +1000, Paul Mackerras wrote:
> On Sun, May 10, 2020 at 01:18:34AM -0400, Qian Cai wrote:
> > It is unsafe to traverse kvm->arch.spapr_tce_tables and
> > stt->iommu_tables without the RCU read lock held. Also, add
> > cond_resched_rcu() in places with the RCU read lock held that could take
> > a while to finish.
>
> This mostly looks fine. The cond_resched_rcu() in kvmppc_tce_validate
> doesn't seem necessary (the list would rarely have more than a few
> dozen entries) and could be a performance problem given that TCE
> validation is a hot-path.
>
> Are you OK with me modifying the patch to take out that
> cond_resched_rcu(), or is there some reason why it's essential that it
> be there?
Feel free to take out that cond_resched_rcu(). Your reasoning makes
sense.
WARNING: multiple messages have this Message-ID (diff)
From: Qian Cai <cai@lca.pw>
To: Paul Mackerras <paulus@ozlabs.org>
Cc: mpe@ellerman.id.au, benh@kernel.crashing.org, aik@ozlabs.ru,
paulmck@kernel.org, linuxppc-dev@lists.ozlabs.org,
kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc/kvm/book3s64/vio: fix some RCU-list locks
Date: Wed, 27 May 2020 01:22:45 +0000 [thread overview]
Message-ID: <20200527012245.GJ991@lca.pw> (raw)
In-Reply-To: <20200527011323.GA293451@thinks.paulus.ozlabs.org>
On Wed, May 27, 2020 at 11:13:23AM +1000, Paul Mackerras wrote:
> On Sun, May 10, 2020 at 01:18:34AM -0400, Qian Cai wrote:
> > It is unsafe to traverse kvm->arch.spapr_tce_tables and
> > stt->iommu_tables without the RCU read lock held. Also, add
> > cond_resched_rcu() in places with the RCU read lock held that could take
> > a while to finish.
>
> This mostly looks fine. The cond_resched_rcu() in kvmppc_tce_validate
> doesn't seem necessary (the list would rarely have more than a few
> dozen entries) and could be a performance problem given that TCE
> validation is a hot-path.
>
> Are you OK with me modifying the patch to take out that
> cond_resched_rcu(), or is there some reason why it's essential that it
> be there?
Feel free to take out that cond_resched_rcu(). Your reasoning makes
sense.
next prev parent reply other threads:[~2020-05-27 1:22 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-10 5:18 [PATCH] powerpc/kvm/book3s64/vio: fix some RCU-list locks Qian Cai
2020-05-10 5:18 ` Qian Cai
2020-05-10 5:18 ` Qian Cai
2020-05-27 1:13 ` Paul Mackerras
2020-05-27 1:13 ` Paul Mackerras
2020-05-27 1:13 ` Paul Mackerras
2020-05-27 1:22 ` Qian Cai [this message]
2020-05-27 1:22 ` Qian Cai
2020-05-27 1:22 ` Qian Cai
2020-05-27 4:19 ` Paul Mackerras
2020-05-27 4:19 ` Paul Mackerras
2020-05-27 4:19 ` Paul Mackerras
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=20200527012245.GJ991@lca.pw \
--to=cai@lca.pw \
--cc=aik@ozlabs.ru \
--cc=benh@kernel.crashing.org \
--cc=kvm-ppc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mpe@ellerman.id.au \
--cc=paulmck@kernel.org \
--cc=paulus@ozlabs.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 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.