65 messages in org.freebsd.freebsd-smpRe: SMP meeting summary| From | Sent On | Attachments |
|---|---|---|
| Jason Evans | Jun 24, 2000 11:56 pm | |
| Daniel Eischen | Jun 25, 2000 6:58 am | |
| Terry Lambert | Jun 25, 2000 10:12 am | |
| Terry Lambert | Jun 25, 2000 10:36 am | |
| Julian Elischer | Jun 25, 2000 10:41 am | |
| Poul-Henning Kamp | Jun 25, 2000 11:07 am | |
| Nate Williams | Jun 25, 2000 9:41 pm | |
| Frank Mayhar | Jun 25, 2000 11:27 pm | |
| Frank Mayhar | Jun 25, 2000 11:31 pm | |
| Luoqi Chen | Jun 26, 2000 9:46 am | |
| Arun Sharma | Jun 26, 2000 9:47 am | |
| Jason Evans | Jun 26, 2000 11:06 am | |
| Matthew Dillon | Jun 26, 2000 12:26 pm | |
| Matthew Dillon | Jun 26, 2000 12:48 pm | |
| John Sconiers | Jun 26, 2000 12:56 pm | |
| Matthew Dillon | Jun 26, 2000 1:07 pm | |
| Luoqi Chen | Jun 26, 2000 1:13 pm | |
| Doug Rabson | Jun 26, 2000 1:26 pm | |
| Jason Evans | Jun 26, 2000 2:56 pm | |
| Jason Evans | Jun 26, 2000 3:14 pm | |
| Daniel Eischen | Jun 26, 2000 4:59 pm | |
| Luoqi Chen | Jun 26, 2000 7:14 pm | |
| Jason Evans | Jun 26, 2000 7:55 pm | |
| Joe Eykholt | Jun 26, 2000 8:09 pm | |
| Greg Lehey | Jun 27, 2000 8:00 pm | |
| Jason Evans | Jun 27, 2000 8:25 pm | |
| Daniel Eischen | Jun 27, 2000 8:26 pm | |
| Greg Lehey | Jun 27, 2000 9:59 pm | |
| Greg Lehey | Jun 27, 2000 10:11 pm | |
| Terry Lambert | Jun 28, 2000 4:15 pm | |
| Terry Lambert | Jun 28, 2000 4:18 pm | |
| Terry Lambert | Jun 28, 2000 4:37 pm | |
| Terry Lambert | Jun 28, 2000 4:51 pm | |
| Arun Sharma | Jun 28, 2000 9:43 pm | |
| Greg Lehey | Jul 2, 2000 7:15 pm | |
| Daniel Eischen | Jul 3, 2000 3:23 am | |
| Greg Lehey | Jul 3, 2000 3:30 am | |
| Jeroen C. van Gelderen | Jul 3, 2000 7:55 am | |
| Chuck Paterson | Jul 3, 2000 8:28 am | |
| Chuck Paterson | Jul 3, 2000 8:47 am | |
| Frank Mayhar | Jul 3, 2000 8:49 am | |
| Greg Lehey | Jul 3, 2000 4:08 pm | |
| David Scheidt | Jul 3, 2000 4:35 pm | |
| Joe Eykholt | Jul 3, 2000 4:47 pm | |
| Greg Lehey | Jul 3, 2000 4:52 pm | |
| Joe Eykholt | Jul 3, 2000 4:58 pm | |
| Greg Lehey | Jul 3, 2000 5:26 pm | |
| Joe Eykholt | Jul 3, 2000 5:41 pm | |
| Chuck Paterson | Jul 3, 2000 7:17 pm | |
| Daniel Eischen | Jul 3, 2000 7:25 pm | |
| Daniel Eischen | Jul 3, 2000 7:35 pm | |
| Greg Lehey | Jul 3, 2000 7:39 pm | |
| Daniel Eischen | Jul 3, 2000 7:41 pm | |
| Chuck Paterson | Jul 3, 2000 8:40 pm | |
| Alfred Perlstein | Jul 3, 2000 10:08 pm | |
| Greg Lehey | Jul 3, 2000 10:37 pm | |
| Peter Wemm | Jul 4, 2000 2:43 pm | |
| Greg Lehey | Jul 4, 2000 3:58 pm | |
| Peter Wemm | Jul 4, 2000 4:06 pm | |
| Terry Lambert | Jul 5, 2000 3:38 pm | |
| Terry Lambert | Jul 5, 2000 4:00 pm | |
| Terry Lambert | Jul 5, 2000 4:06 pm | |
| Terry Lambert | Jul 5, 2000 4:10 pm | |
| Alfred Perlstein | Jul 5, 2000 4:29 pm | |
| Terry Lambert | Jul 6, 2000 4:50 pm |
| Subject: | Re: SMP meeting summary | |
|---|---|---|
| From: | Greg Lehey (gr...@lemis.com) | |
| Date: | Jul 3, 2000 7:39:08 pm | |
| List: | org.freebsd.freebsd-smp | |
On Monday, 3 July 2000 at 20:18:00 -0600, Chuck Paterson wrote:
I'm not sure we're talking about the same thing, but if so I must be missing something. If I'm waiting on a mutex, I still need to reacquire it on wakeup, don't I? In that case, only the first process to be scheduled will actually get the mutex, and the others will block again.
Yes, you need to acquire the mutex on wakeup, but likely one process will run acquiring and releasing the mutex in an uncontested fashion before other processes run and do the same thing.
Hmmm. Yes, I suppose that would happen in a single processor environment.
In general there ought not to be multiple processes piling up on a mutex. If there are and for some reason they can't be fixed then these particular mutexs are going to dictate how this area is handled. Once we have these cases in hand we can make some decisions as to how to proceed.
In my experience, I've seen mutexes used for long-term waits, and I don't see any a priori reason not to do so. Of course, if we make design decisions based on the assumption that all waits will be short, then we will have a reason, but it won't be a good one.
Before you say that long-term waits are evil, note that we're probably talking about different kinds of waits. Obviously anything that threatens to keep the system idle while it waits is bad, but a replacement for tsleep(), say, can justifiably wait for a long time.
A replacement for tsleep is not a mutex, but in Solaris parlance a conditional variable.
I think we have a certain problem with terminology, and it seems to be clouding the discussion. The big difference between the BSD/OS sleep mutex and the semaphores we used at Tandem (amongst other things for long-term waits) wasn't the counter (which was always set to 1) but the name.
The uses are different, one is for locking a resource, the other is waiting on a synch event. A conditional variable, like the sleep queues has a mutex associated with it. This mutex is not held except while processing the event, both by the process waiting and the process doing the activation.
This is a different paradigm from the one we used.
I don't think it is a good idea to assume that the heuristics for waking up tsleep / conditional variables is going to be anything like those seen with mutexs.
Maybe. I need to let this go through my head. Just because we found it to be the right idea at Tandem doesn't mean it's the right idea here. I've never been able to understand the advantages of conditional variables, which may be my viewpoint, or it may be some basic lack of understanding.
Since things have been cuts and pasted I'll say again I don't have a good idea what the right answer is on any of this. I do believe we need to get what we have running, instrument it, and reach some decisions.
Agreed entirely. At the moment the discussion is academic. When we've done the implementation, we'll have a much better idea about what we really want^H^H^H^Hneed.
Greg
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