Date: Tue, 2 Dec 2003 12:45:28 +0300 (MSK) From: Igor Sysoev <is@rambler-co.ru> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-smp@freebsd.org Subject: RE: halting HTT Message-ID: <Pine.BSF.4.21.0312021244100.17170-100000@is> In-Reply-To: <XFMail.20031201155959.jhb@FreeBSD.org>
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On Mon, 1 Dec 2003, John Baldwin wrote: > On 01-Dec-2003 Igor Sysoev wrote: > > I had noticed that on Nov 11, 2003 in src/sys/i386/i386/mp_machdep.c > > HTT CPUs are not halted by default. What is the reason to do it ? > > Is it not better to allow logical CPUs to handle interrupts ? > > HTT CPUs were halted by default because we needed them to always be > used to work around other bugs. Since the other bugs are fixed, we > no longer need HTT CPUs unless the user wants them. If you disable > HT in the BIOS for example, we no longer probe them. Thus, it doesn't > make sense to halt the CPUs if the user has explicitly asked for > them. Thank you for explanation. But what is about a handling interrupts by logical CPUs ? Could you recommend it or not ? I think that a using logical CPUs decreases an overhead while handling interrupts - main CPUs do not need to switch contexts. > > Besides if I try to halting logical CPUs by machdep.hlt_cpus=10 or > > machdep.hlt_logical_cpus=1 then computer is partially freezed, i.e > > top that running in ssh session could contunue to run but I can not > > login to computer anymore. > > > > I'm using 5.1-CURRENT from 2003.11.28.00.00.00 and > > machdep.logical_cpus_mask=10 > > I do not know why your machine freezes when you halt the logical > CPUs. I think it was because of SCHED_ULE. When I rebuild kernel with SCHED_4BSD I can disable logical CPUs without freezing. I added Jeff Roberson to CC to notify him about SCHED_ULE freezing. Igor Sysoev http://sysoev.ru/en/
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