Messages in this thread | | | From | Eric Lacombe <> | Subject | Re: [x86] fs, gs purpose & multicore prog | Date | Sat, 6 Sep 2008 01:09:52 +0200 |
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Thanks again ;)
On Vendredi 05 Septembre 2008 16:51:39 Jeremy Fitzhardinge wrote: > Eric Lacombe wrote: [...] > >>> - What is the purpose of MSR_FS_BASE and MSR_GS_BASE ? > >>> (I thought they were filled with "gdt[fs_entry].base") > >> > >> On 64-bit, the GDT isn't large enough to hold a 64-bit offset, so it > >> only stores the low 32-bits. When you load a segment register with a > >> selector, it picks up from the gdt. If you want a full 64-bit offset, > >> you need to write it to the msr. > > > > Ok, I just saw that a 64-bit base in segment descriptor is only available > > for the system descriptor. > > Yes, the IDT has double-wide entries to fit 64-bit values, but they > didn't extend that to the GDT. Or something - I last looked at this a > couple of months ago, and it never sticks in my brain for long.
It seems, there also are the TSS and LDT.
> > > Ok, but how does the kernel technically run tasks on different processor > > (or core)? My question was ambiguous, I was not assuming that I knew how > > multiprocessor works. > > That's a very broad question. A good proportion of the core kernel code > is dedicated to doing just that. Very roughly, at boot time it brings > up all the cpus, and they more or less run independently each looking > for work to do in the form of processes waiting to run on the run > queue. They collectively run the scheduler algorithms to work out who > runs what when; almost everything run in the kernel is a task - both > usermode processes and kernel threads. Except for the stuff which isn't.
I know these things ;) but what I wanted to know is the "x86 architectural details". In fact, I saw that during the machine init the BIOS select a cpu on the bus to be the BSP (bootstrap proc). The others are then the APs (Appli proc). Then the kernel runs on the BSP. What I wonder is how the kernel gives execution flow to the APs.
Thanks.
Eric
> > J
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