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Re: Quick question.
I said - it WORKS. 1 spin - warning - someone opens system and kills a run away process... Never saw 2 spins (because first one was killed before second one). Btw, such systems (2 CPU) are even more stable in case of run away device drivers. I saw: - run away tomcat server - run away CA agent (!@#$) - run away ssh daemon - run away sandmail All regular, at some periods of time. And all processed without any system degradation because of a few CPU's. The same run-aways on 1 CPU systems caused visible degradation. It is all mattter of trade-off - if I must select 1 threaded or 2 threaded P-IV, I'll select 2 threaded; if I must select from $900 1 CPU and $1100 2 CPU server, I select 2 CPU one. ----- Original Message ----- From: "Paul Jakma" <email@example.com> To: "Alexei Roudnev" <firstname.lastname@example.org> Cc: "Michel Py" <email@example.com>; "Nanog" <firstname.lastname@example.org> Sent: Tuesday, August 03, 2004 11:39 PM Subject: Re: Quick question. > On Tue, 3 Aug 2004, Alexei Roudnev wrote: > > > It is not mad idea - 2 CPU servers are not sugnificantly more > > expansive as 1CPU (and notice, we count P-IV MMultiThread as 2 CPU) > > Well, you have to compare like for like, so system with multiple CPUs > versus exact system without. No diffference in cost, other than for > the CPUs. > > And if you want reliability, you're not going to be buying your > machines from the nearest Lidl (unless your application is engineered > to take advantage of dozens of cheap throwaway PCs). > > > but increases system redundancy to the run-away processes. Of > > course, it is not hardware redundancy, but it REALLY works. > > Not really.. this is a resource exhaustion problem, and you can not > cure this, given buggy apps, by throwing more CPUs at it. > > Let's say you have some multi-process or multi-threaded application > which regularly spawns/forks new processes/threads, but it is buggy > and prone to having individual processes/threads spin. > > So one spins, but you still have plenty of CPU time left cause you > have two CPUs. Another spins, and the machine starts to crawl. So you > solve this problem by upgrading to a quad-SMP machine. And guess what > happens? :) > > Sure, there are some application bugs you can mask a wee bit with > SMP, but it's not much cop, its not a solution, and you need > an infinite-SMP machine to guarantee that a bad application > can never hog all CPU time. > > What you really want is a good OS with: > > - a good scheduler (to prevent spinning tasks from starving other > tasks) > > - ability to set resource limits, ie per-task and/or per-user (if > your apps run under dedicated user accounts) limits on cpu time, > resident memory, etc.. > > Both of these will allow you to constrain the impact bad tasks can > have on the system, whether your machine is 1, 2, ... or n CPUs. > > The real solution though is to fix the buggy application. > > regards, > -- > Paul Jakma email@example.com firstname.lastname@example.org Key ID: 64A2FF6A > Fortune: > The life which is unexamined is not worth living. > -- Plato