Messages in this thread Patch in this message |  | | Date | Wed, 04 Oct 2000 11:31:35 -0400 | From | Brian Gerst <> | Subject | Re: wasting time on page fault |
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Andi Kleen wrote: > > On Wed, Oct 04, 2000 at 11:00:41AM -0400, Brian Gerst wrote: > > Mikulas Patocka wrote: > > > > > > Hi. > > > > > > arch/i386/kernel/entry.S > > > xchgl %eax, ORIG_EAX(%esp) # orig_eax (get the error code. ) > > > movl %esp,%edx > > > xchgl %ecx, ES(%esp) # get the address and save es. > > > pushl %eax # push the error code > > > > > > xchg with memory operand has implicit lock prefix and is slooooooow. It is > > > really bad idea to have it in page fault handler. > > > > Thank the small register set of the x86 for this. If you can come up > > with a way to do it in fewer cycles and preserve all the registers and > > stack layout, your input is welcome. > > You don't need to preserve any registers which are not %eax, they are already > saved. There are tons of ways to do it via the stack or with a temporary > register.
You are correct. That's what I get for posting before my normal dose of caffeine. Something like this should work (untested):
--- entry.S Tue Oct 3 13:05:07 2000 +++ entry.S.new Wed Oct 4 11:29:45 2000 @@ -305,16 +305,18 @@ pushl %ebx cld movl %es,%ecx - xchgl %eax, ORIG_EAX(%esp) # orig_eax (get the error code. ) + movl ORIG_EAX(%esp), %esi # get the error code + movl ES(%esp), %edi # get the address movl %esp,%edx - xchgl %ecx, ES(%esp) # get the address and save es. - pushl %eax # push the error code - pushl %edx + movl %eax, ORIG_EAX(%esp) + movl %ecx, ES(%esp) + pushl %esi # push the error code + pushl %edx # push pt_regs pointer movl $(__KERNEL_DS),%edx movl %edx,%ds movl %edx,%es GET_CURRENT(%ebx) - call *%ecx + call *%edi addl $8,%esp jmp ret_from_exception
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