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From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>,
	Ian Jackson <iwj@xenproject.org>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	Julien Grall <julien@xen.org>,
	Dario Faggioli <dfaggioli@suse.com>,
	Xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH 4/6] x86/trace: Reduce stack usage from HVMTRACE_ND()
Date: Mon, 20 Sep 2021 15:00:12 +0200	[thread overview]
Message-ID: <f52efb10-7762-9828-e8c4-ce2d00acdff5@suse.com> (raw)
In-Reply-To: <e116bff4-9080-1629-221d-f2ba3255d03e@citrix.com>

On 20.09.2021 13:02, Andrew Cooper wrote:
> On 20/09/2021 10:05, Jan Beulich wrote:
>> On 17.09.2021 10:45, Andrew Cooper wrote:
>>> It is pointless to write all 6 entries and only consume the useful subset.
>>> bloat-o-meter shows quite how obscene the overhead is in vmx_vmexit_handler(),
>>> weighing in at 11% of the function arranging unread zeroes on the stack, and
>>> 8% for svm_vmexit_handler().
>>>
>>>   add/remove: 0/0 grow/shrink: 0/20 up/down: 0/-1867 (-1867)
>>>   Function                                     old     new   delta
>>>   hvm_msr_write_intercept                     1049    1033     -16
>>>   vmx_enable_intr_window                       238     214     -24
>>>   svm_enable_intr_window                       337     313     -24
>>>   hvmemul_write_xcr                            115      91     -24
>>>   hvmemul_write_cr                             350     326     -24
>>>   hvmemul_read_xcr                             115      91     -24
>>>   hvmemul_read_cr                              146     122     -24
>>>   hvm_mov_to_cr                                438     414     -24
>>>   hvm_mov_from_cr                              253     229     -24
>>>   vmx_intr_assist                             1150    1118     -32
>>>   svm_intr_assist                              459     427     -32
>>>   hvm_rdtsc_intercept                          138     106     -32
>>>   hvm_msr_read_intercept                       898     866     -32
>>>   vmx_vmenter_helper                          1142    1094     -48
>>>   vmx_inject_event                             813     765     -48
>>>   svm_vmenter_helper                           238     190     -48
>>>   hvm_hlt                                      197     146     -51
>>>   svm_inject_event                            1678    1614     -64
>>>   svm_vmexit_handler                          5880    5416    -464
>>>   vmx_vmexit_handler                          7281    6473    -808
>>>   Total: Before=3644184, After=3642317, chg -0.05%
>>>
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> 
> Thanks, but this is buggy.  There are direct callers of HVMTRACE_ND()
> which need adjustments too.

Is this really "buggy" and "need" and not merely "incomplete" and
"want"? (Just for my own understanding in terms of what I may have
overlooked.)

Jan



  reply	other threads:[~2021-09-20 13:00 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-17  8:45 [PATCH 0/6] xen/trace: Fix leakage of uninitialised stack into the tracebuffer Andrew Cooper
2021-09-17  8:45 ` [PATCH 1/6] xen/trace: Don't over-read trace objects Andrew Cooper
2021-09-17 12:58   ` Jan Beulich
2021-09-17 13:26     ` Andrew Cooper
2021-09-20  8:00       ` Jan Beulich
2021-09-20 10:24         ` Andrew Cooper
2021-09-17  8:45 ` [PATCH 2/6] xen/memory: Remove tail padding from TRC_MEM_* records Andrew Cooper
2021-09-17 13:04   ` Jan Beulich
2021-09-17  8:45 ` [PATCH 3/6] xen/credit2: Remove tail padding from TRC_CSCHED2_* records Andrew Cooper
2021-09-17 13:10   ` Jan Beulich
2021-09-17 13:28     ` Andrew Cooper
2021-09-17  8:45 ` [PATCH 4/6] x86/trace: Reduce stack usage from HVMTRACE_ND() Andrew Cooper
2021-09-20  9:05   ` Jan Beulich
2021-09-20 11:02     ` Andrew Cooper
2021-09-20 13:00       ` Jan Beulich [this message]
2021-09-17  8:45 ` [PATCH 5/6] xen/credit2: Clean up trace handling Andrew Cooper
2021-09-20  9:11   ` Jan Beulich
2021-09-17  8:45 ` [PATCH 6/6] xen/trace: Minor code cleanup Andrew Cooper
2021-09-20  9:15   ` Jan Beulich

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