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Re: [PATCH v2.1 RFC 17/12] xen/trace: Drop cycles parameter
- To: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 21 Sep 2021 21:08:05 +0100
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Not a patch, but an RFC idea for one...
It occurred to me that the cycles parameter from __trace_var() and
friends is pointless, as the cycles bit is encoded in the top bit of the
event field anyway, and passed in the adjacent parameter.
Dropping the cycles parameter results in +85/-1029 (-944) net change.
The common change in callers is e.g. from:
lea 0x3c(%rsp),%rcx
mov $0x4,%edx
mov $0x1,%esi
mov $0x10f002,%edi
mov %ebp,0x3c(%rsp)
callq ffff82d04022ea20 <__trace_var>
to this:
lea 0x3c(%rsp),%rdx
mov $0x4,%esi
mov $0x8010f002,%edi
mov %ebp,0x3c(%rsp)
callq ffff82d04022ea20 <__trace_var>
Just sprinkling "| TRC_HD_CYCLE_FLAG" over the place makes things a
little bit unwieldy.
Instead, I was thinking of implementing trace() (and a thin trace_time()
wrapper) mirroring the "new API" in patch 14. Half of the trace_var()
users should be __trace_var() already because of living inside a
tb_init_done conditional, and the rest are actually opencoded TRACE()
taking no extra data.
Thoughts?
~Andrew
|
