Messages in this thread | | | Date | Mon, 13 Jan 2014 13:21:44 -0800 | From | Cody P Schafer <> | Subject | Re: [PATCH 2/3] perf: clarify comment regarding event merging |
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On 01/10/2014 01:36 AM, Peter Zijlstra wrote: > On Thu, Jan 09, 2014 at 03:51:31PM -0800, Cody P Schafer wrote: >> There are actually 2 things about software events that allow us to >> merge them: they never fail to schedule _and_ they have transaction >> handlers we can (and do, when they are added to !sw groups) ignore. Note >> both of these in the comment on adding sw events to !sw groups. > > The latter is a direct consequence of the former. Since they can always > be scheduled, they don't need any schedulability testing, and therefore > the transaction stuff is useless.
Right. I guess what I was getting at were the 2 types of "schedulability": 1. individual event schedulability (ie: "did add() return an error?") 2. txn schedulability (ie: "did commit_txn() return an error?")
I'm in the process of adding a pmu which guarantees #1, but not #2 (it essentially provides access to some always-running counters which can be atomically copied in groups). As a result, I'm teasing apart some of the special casing done for sw events.
This will probably make a bit more sense with some better terminology on my part and some actual code. I'll update and resend later.
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