Re: Top not showing 4 cpus on 2 xeons with HT
Adrian Chadd wrote: > anyone have any recent information about this? some people say "HT > sucks for almost all workloads", others say "recent scheduler > improvements make HT more useful".. is there anything reasonably > authoritative? No, because it depends on your applications and workload. for some it is better, for some it is not. Therefore it's best you try both variants on your own machine with your own applications and measure the difference. There's one rule of thumb, however: If you only have one HTT-capable processor, then a UP kernel will almost always be the better option, because the locking overhead of an SMP kernel will probably outweigh any advantages of HTT. On the other hand, if you have a real SMP system (i.e. multiple processors or cores, not counting HTT), then you will want to use an SMP kernel anyway. In that case, enabling HTT will probably not hurt -- _but_ there have been reports of some people that HTT hurts in such a case for certain kinds of applications (I think databases was one of them, but I don't remember exactly). Anyway, there are exceptions to any rule, so you should measure yourself. Personally I disable HTT on all of my machines because of the security issue (jails do _not_ help here at all!), and speed improvements -- if any -- are marginally small, according to my own measurements. In fact I had a hard time finding any reproducible measurable improvements at all for my typical workloads; consequently my decision was governed by the security issue. Best regards Oliver -- Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M. Handelsregister: Registergericht Muenchen, HRA 74606, Geschäftsfuehrung: secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün- chen, HRB 125758, Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart FreeBSD-Dienstleistungen, -Produkte und mehr: http://www.secnetix.de/bsd "Perl will consistently give you what you want, unless what you want is consistency." -- Larry Wall ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Top not showing 4 cpus on 2 xeons with HT
On 25/04/07, Tom Evans <[EMAIL PROTECTED]> wrote: Yes, quite easily. anyone have any recent information about this? some people say "HT sucks for almost all workloads", others say "recent scheduler improvements make HT more useful".. is there anything reasonably authoritative? adrian ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Top not showing 4 cpus on 2 xeons with HT
On Wed, 25 Apr 2007 15:26:02 +0400, "Artem Kuchin" <[EMAIL PROTECTED]> wrote: > I am just wondering if it is normal. > I have two xeon processors with HT on each of them. > When loading kernel says that 4 cpu's are found, > but when i do top i can see only 0 or 2 in the C > column. never 1 or 3. Is it normal? Hyperthreading has been disabled by default for quite some time now. More info (including ways to reenable HTT) can be found here: http://security.freebsd.org/advisories/FreeBSD-SA-05:09.htt.asc Regards, Søren Klintrup ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Top not showing 4 cpus on 2 xeons with HT
On Wed, 2007-04-25 at 16:50 +0400, Artem Kuchin wrote: > Richard Tector wrote: > > Artem Kuchin wrote: > >> I am just wondering if it is normal. > >> I have two xeon processors with HT on each of them. > >> When loading kernel says that 4 cpu's are found, > >> but when i do top i can see only 0 or 2 in the C > >> column. never 1 or 3. Is it normal? > >> > >> FreeBSD 6.2-STABLE (cvsed 1 day ago) > > If I remember correctly, HT is disabled by default for security > > reasons but there should be a sysctl to enable it. I believe there is > > also a paper by Colin Percival on the issue. > > > ahh, heck, i'll take my chances. I've read the paper and the attack > seem to me almost unreal. Also, everybody is in the jail on the server. > > > Note that in a lot of common loads, the use of HT with the standard > > scheduler does not yield any real benefits. > > Hmm. I just turned it on and already see that hosts are running generally > faster (it is a hosting server, 100+ site). No numbers though. It just > *SEEMS* faster. Anyway, it cannot make thing slower for sure, or > can it? > > -- > Regards, > Artem > > > > ___ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "[EMAIL PROTECTED]" Yes, quite easily. signature.asc Description: This is a digitally signed message part
Re: Top not showing 4 cpus on 2 xeons with HT
Richard Tector wrote: Artem Kuchin wrote: I am just wondering if it is normal. I have two xeon processors with HT on each of them. When loading kernel says that 4 cpu's are found, but when i do top i can see only 0 or 2 in the C column. never 1 or 3. Is it normal? FreeBSD 6.2-STABLE (cvsed 1 day ago) If I remember correctly, HT is disabled by default for security reasons but there should be a sysctl to enable it. I believe there is also a paper by Colin Percival on the issue. ahh, heck, i'll take my chances. I've read the paper and the attack seem to me almost unreal. Also, everybody is in the jail on the server. Note that in a lot of common loads, the use of HT with the standard scheduler does not yield any real benefits. Hmm. I just turned it on and already see that hosts are running generally faster (it is a hosting server, 100+ site). No numbers though. It just *SEEMS* faster. Anyway, it cannot make thing slower for sure, or can it? -- Regards, Artem ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Top not showing 4 cpus on 2 xeons with HT
Artem Kuchin wrote: I am just wondering if it is normal. I have two xeon processors with HT on each of them. When loading kernel says that 4 cpu's are found, but when i do top i can see only 0 or 2 in the C column. never 1 or 3. Is it normal? FreeBSD 6.2-STABLE (cvsed 1 day ago) If I remember correctly, HT is disabled by default for security reasons but there should be a sysctl to enable it. I believe there is also a paper by Colin Percival on the issue. Note that in a lot of common loads, the use of HT with the standard scheduler does not yield any real benefits. Regards, Richard ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Top not showing 4 cpus on 2 xeons with HT
I am just wondering if it is normal. I have two xeon processors with HT on each of them. When loading kernel says that 4 cpu's are found, but when i do top i can see only 0 or 2 in the C column. never 1 or 3. Is it normal? FreeBSD 6.2-STABLE (cvsed 1 day ago) -- Regards. Artem ___ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[EMAIL PROTECTED]"
