From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <JBeulich@suse.com>,
Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Wei Liu <wei.liu2@citrix.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Tim Deegan <tim@xen.org>, Ian Jackson <Ian.Jackson@eu.citrix.com>,
Julien Grall <julien.grall@arm.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH 1/3] xen: drop in_atomic()
Date: Wed, 22 May 2019 15:01:03 +0200 [thread overview]
Message-ID: <c3d83d55-b987-bc9b-5af2-00474f696a02@suse.com> (raw)
On 22/05/2019 14:34, Jan Beulich wrote:
>>>> On 22.05.19 at 12:19, <jgross@suse.com> wrote:
>> On 22/05/2019 12:10, Jan Beulich wrote:
>>>>>> On 22.05.19 at 11:45, <jgross@suse.com> wrote:
>>>> --- a/xen/arch/x86/hvm/hvm.c
>>>> +++ b/xen/arch/x86/hvm/hvm.c
>>>> @@ -3185,22 +3185,6 @@ static enum hvm_translation_result __hvm_copy(
>>>>
>>>> ASSERT(is_hvm_vcpu(v));
>>>>
>>>> - /*
>>>> - * XXX Disable for 4.1.0: PV-on-HVM drivers will do grant-table ops
>>>> - * such as query_size. Grant-table code currently does
>> copy_to/from_guest
>>>> - * accesses under the big per-domain lock, which this test would
>> disallow.
>>>> - * The test is not needed until we implement sleeping-on-waitqueue when
>>>> - * we access a paged-out frame, and that's post 4.1.0 now.
>>>> - */
>>>> -#if 0
>>>> - /*
>>>> - * If the required guest memory is paged out, this function may sleep.
>>>> - * Hence we bail immediately if called from atomic context.
>>>> - */
>>>> - if ( in_atomic() )
>>>> - return HVMTRANS_unhandleable;
>>>> -#endif
>>>
>>> Dealing with this TODO item is of course much appreciated, but
>>> should it really be deleted altogether? The big-domain-lock issue
>>> is gone afair, in which case dropping the #if 0 would seem
>>> possible to me, even if it's not strictly needed without the sleep-
>>> on-waitqueue behavior mentioned.
>>
>> Question is whether it is worth to keep it resulting in the need to
>> keep preempt_count() as well.
>
> Well, personally I think keeping it is a small price to pay. But seeing
> Andrew's R-b he clearly thinks different. And just to be clear - I
> don't really want to veto this change, as at the same time it's also
> easy enough to put back if need be. But I'd like this to be give a
> 2nd consideration at least.
Completely understandable.
I just stumbled over that when I needed to introduce rcu_read_lock()
usage in some hot paths for my core scheduling series and I wanted to
understand the performance implications for adding those calls.
Juergen
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
WARNING: multiple messages have this Message-ID (diff)
From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <JBeulich@suse.com>,
Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Wei Liu <wei.liu2@citrix.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Tim Deegan <tim@xen.org>, Ian Jackson <Ian.Jackson@eu.citrix.com>,
Julien Grall <julien.grall@arm.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH 1/3] xen: drop in_atomic()
Date: Wed, 22 May 2019 15:01:03 +0200 [thread overview]
Message-ID: <c3d83d55-b987-bc9b-5af2-00474f696a02@suse.com> (raw)
Message-ID: <20190522130103.2bQdffFx80BqDqeojqvohkvf2HZMJa_83M9zh1GiWoU@z> (raw)
On 22/05/2019 14:34, Jan Beulich wrote:
>>>> On 22.05.19 at 12:19, <jgross@suse.com> wrote:
>> On 22/05/2019 12:10, Jan Beulich wrote:
>>>>>> On 22.05.19 at 11:45, <jgross@suse.com> wrote:
>>>> --- a/xen/arch/x86/hvm/hvm.c
>>>> +++ b/xen/arch/x86/hvm/hvm.c
>>>> @@ -3185,22 +3185,6 @@ static enum hvm_translation_result __hvm_copy(
>>>>
>>>> ASSERT(is_hvm_vcpu(v));
>>>>
>>>> - /*
>>>> - * XXX Disable for 4.1.0: PV-on-HVM drivers will do grant-table ops
>>>> - * such as query_size. Grant-table code currently does
>> copy_to/from_guest
>>>> - * accesses under the big per-domain lock, which this test would
>> disallow.
>>>> - * The test is not needed until we implement sleeping-on-waitqueue when
>>>> - * we access a paged-out frame, and that's post 4.1.0 now.
>>>> - */
>>>> -#if 0
>>>> - /*
>>>> - * If the required guest memory is paged out, this function may sleep.
>>>> - * Hence we bail immediately if called from atomic context.
>>>> - */
>>>> - if ( in_atomic() )
>>>> - return HVMTRANS_unhandleable;
>>>> -#endif
>>>
>>> Dealing with this TODO item is of course much appreciated, but
>>> should it really be deleted altogether? The big-domain-lock issue
>>> is gone afair, in which case dropping the #if 0 would seem
>>> possible to me, even if it's not strictly needed without the sleep-
>>> on-waitqueue behavior mentioned.
>>
>> Question is whether it is worth to keep it resulting in the need to
>> keep preempt_count() as well.
>
> Well, personally I think keeping it is a small price to pay. But seeing
> Andrew's R-b he clearly thinks different. And just to be clear - I
> don't really want to veto this change, as at the same time it's also
> easy enough to put back if need be. But I'd like this to be give a
> 2nd consideration at least.
Completely understandable.
I just stumbled over that when I needed to introduce rcu_read_lock()
usage in some hot paths for my core scheduling series and I wanted to
understand the performance implications for adding those calls.
Juergen
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
next reply other threads:[~2019-05-22 13:01 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-22 13:01 Juergen Gross [this message]
2019-05-22 13:01 ` [Xen-devel] [PATCH 1/3] xen: drop in_atomic() Juergen Gross
-- strict thread matches above, loose matches on Subject: below --
2019-05-22 9:45 [PATCH 0/3] tune preempt_[dis|en]able() Juergen Gross
2019-05-22 9:45 ` [PATCH 1/3] xen: drop in_atomic() Juergen Gross
2019-05-22 9:58 ` Andrew Cooper
2019-05-22 10:10 ` Jan Beulich
2019-05-24 5:41 ` Juergen Gross
2019-05-24 6:38 ` Jan Beulich
2019-05-24 8:34 ` Juergen Gross
2019-05-24 8:39 ` Jan Beulich
2019-05-24 12:30 ` Andrew Cooper
2019-05-24 12:35 ` Jan Beulich
[not found] ` <5CE52014020000780023147E@suse.com>
2019-05-22 10:19 ` Juergen Gross
2019-05-22 12:34 ` Jan Beulich
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=c3d83d55-b987-bc9b-5af2-00474f696a02@suse.com \
--to=jgross@suse.com \
--cc=George.Dunlap@eu.citrix.com \
--cc=Ian.Jackson@eu.citrix.com \
--cc=JBeulich@suse.com \
--cc=andrew.cooper3@citrix.com \
--cc=julien.grall@arm.com \
--cc=konrad.wilk@oracle.com \
--cc=roger.pau@citrix.com \
--cc=sstabellini@kernel.org \
--cc=tim@xen.org \
--cc=wei.liu2@citrix.com \
--cc=xen-devel@lists.xenproject.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).