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From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH 8/9] x86/hypercall: Merge the hypercall arg tables
Date: Wed, 03 Aug 2016 09:28:53 -0600	[thread overview]
Message-ID: <57A229D50200007800102584@prv-mh.provo.novell.com> (raw)
In-Reply-To: <5f0f2c99-e5dd-15b4-7adf-043d0f047a0b@citrix.com>

>>> On 03.08.16 at 17:15, <andrew.cooper3@citrix.com> wrote:
> On 03/08/16 16:12, Jan Beulich wrote:
>>>>> On 18.07.16 at 11:51, <andrew.cooper3@citrix.com> wrote:
>>> For the same reason as c/s 33a231e3f "x86/HVM: fold hypercall tables" and
>>> (TODO - changeset) "x86/pv: Merge the pv hypercall tables", this removes the
>>> risk of accidentally updating only one of the tables.
>> Based on this argument perhaps hypercall and args tables should
>> get folded too, but I guess that's a work item for another day.
> 
> That is rather harder to do.  I thought about it, but couldn't find a
> neat way of doing it.
> 
> The call table is an array of pointers, while the args table is an array
> of bytes.  Merging them would result in excessive padding for alignment
> purposes, unless it was packed, at which point we are calling
> non-aligned function pointers, and taking that associated performance hit.

If we folded everything together (pv, hvm, args), there would be
6 bytes padding per 34 or actual data, so I wouldn't be worried
too much. But I admit that merging hvm and pv tables wouldn't be
entirely trivial.

Jan


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  reply	other threads:[~2016-08-03 15:28 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-18  9:51 [PATCH 0/9] x86: Move the pv hypercall into C Andrew Cooper
2016-07-18  9:51 ` [PATCH 1/9] x86/hypercall: Move some of the hvm hypercall infrastructure into hypercall.h Andrew Cooper
2016-08-02 12:50   ` Jan Beulich
2016-08-02 13:14     ` Andrew Cooper
2016-08-02 13:28       ` Jan Beulich
2016-08-02 14:04         ` Julien Grall
2016-08-02 14:17           ` Jan Beulich
2016-08-02 14:26             ` Julien Grall
2016-08-02 14:54               ` Jan Beulich
2016-08-02 14:59                 ` Andrew Cooper
2016-08-02 15:05                   ` Jan Beulich
2016-08-02 18:43                     ` Stefano Stabellini
2016-08-03  8:53                       ` Jan Beulich
2016-08-03 10:55                         ` Julien Grall
2016-08-03 18:20                           ` Stefano Stabellini
2016-08-04 11:27                             ` Julien Grall
2016-07-18  9:51 ` [PATCH 2/9] x86/pv: Support do_set_segment_base() for compat guests Andrew Cooper
2016-08-02 12:52   ` Jan Beulich
2016-08-02 13:25     ` Andrew Cooper
2016-08-02 13:31       ` Jan Beulich
2016-08-02 13:39         ` Andrew Cooper
2016-08-02 13:47           ` Jan Beulich
2016-07-18  9:51 ` [PATCH 3/9] x86/hypercall: Move the hypercall arg tables into C Andrew Cooper
2016-08-02 12:59   ` Jan Beulich
2016-07-18  9:51 ` [PATCH 4/9] x86/pv: Implement pv_hypercall() in C Andrew Cooper
2016-08-02 13:12   ` Jan Beulich
2016-08-02 14:06     ` Andrew Cooper
2016-08-02 14:19       ` Jan Beulich
2016-08-11 11:57     ` Andrew Cooper
2016-08-11 12:20       ` Jan Beulich
2016-07-18  9:51 ` [PATCH 5/9] x86/hypercall: Move the hypercall tables into C Andrew Cooper
2016-08-02 13:23   ` Jan Beulich
2016-08-02 13:30     ` Andrew Cooper
2016-08-02 13:40       ` Jan Beulich
2016-08-11 12:00         ` Andrew Cooper
2016-07-18  9:51 ` [PATCH 6/9] xen/multicall: Rework arch multicall handling Andrew Cooper
2016-07-20 12:35   ` Julien Grall
2016-08-03 15:02   ` Jan Beulich
2016-08-03 15:12     ` Andrew Cooper
2016-07-18  9:51 ` [PATCH 7/9] x86/pv: Merge the pv hypercall tables Andrew Cooper
2016-08-03 15:07   ` Jan Beulich
2016-08-11 12:36     ` Andrew Cooper
2016-07-18  9:51 ` [PATCH 8/9] x86/hypercall: Merge the hypercall arg tables Andrew Cooper
2016-08-03 15:12   ` Jan Beulich
2016-08-03 15:15     ` Andrew Cooper
2016-08-03 15:28       ` Jan Beulich [this message]
2016-07-18  9:51 ` [PATCH 9/9] x86/hypercall: Reduce the size of the hypercall tables Andrew Cooper
2016-08-03 15:17   ` Jan Beulich

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