On Mon, 20 Jul 2015 10:38:47 +0200 Ingo Molnar <mi...@kernel.org> wrote:
> > * Martin Schwidefsky <schwidef...@de.ibm.com> wrote: > > > diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S > > index 3238893..84062e7 100644 > > --- a/arch/s390/kernel/entry.S > > +++ b/arch/s390/kernel/entry.S > > @@ -178,17 +178,21 @@ _PIF_WORK = (_PIF_PER_TRAP) > > */ > > ENTRY(__switch_to) > > stmg %r6,%r15,__SF_GPRS(%r15) # store gprs of prev task > > - stg %r15,__THREAD_ksp(%r2) # store kernel stack of prev > > - lg %r4,__THREAD_info(%r2) # get thread_info of prev > > - lg %r5,__THREAD_info(%r3) # get thread_info of next > > + lgr %r1,%r2 > > + aghi %r1,__TASK_thread # thread_struct of prev task > > + lg %r4,__TASK_thread_info(%r2) # get thread_info of prev > > + lg %r5,__TASK_thread_info(%r3) # get thread_info of next > > + stg %r15,__THREAD_ksp(%r1) # store kernel stack of prev > > + lgr %r1,%r3 > > + aghi %r1,__TASK_thread # thread_struct of next task > > lgr %r15,%r5 > > aghi %r15,STACK_INIT # end of kernel stack of next > > stg %r3,__LC_CURRENT # store task struct of next > > stg %r5,__LC_THREAD_INFO # store thread info of next > > stg %r15,__LC_KERNEL_STACK # store end of kernel stack > > + lg %r15,__THREAD_ksp(%r1) # load kernel stack of next > > lctl %c4,%c4,__TASK_pid(%r3) # load pid to control reg. 4 > > mvc __LC_CURRENT_PID+4(4,%r0),__TASK_pid(%r3) # store pid of next > > - lg %r15,__THREAD_ksp(%r3) # load kernel stack of next > > lmg %r6,%r15,__SF_GPRS(%r15) # load gprs of next task > > br %r14 > > Btw., I think we'd be slightly better off with the variant I sent: that way > the > offset arithmetics are done in C code and are ready in the relevant registers > by > the time they are used in __switch_to(). If we save any instruction then not many, we are trading additional parameter passing vs. four additional instructions in __switch_to. With this variant the fallout is kept at a minimum which I would prefer at this point. > > > > @@ -417,6 +421,7 @@ ENTRY(pgm_check_handler) > > LAST_BREAK %r14 > > lg %r15,__LC_KERNEL_STACK > > lg %r14,__TI_task(%r12) > > + aghi %r14,__TASK_thread # pointer to thread_struct > > lghi %r13,__LC_PGM_TDB > > tm __LC_PGM_ILC+2,0x02 # check for transaction abort > > jz 2f > > Don't we also need the chunk I have: > > @@ -448,6 +449,7 @@ ENTRY(pgm_check_handler) > nill %r10,0x007f > sll %r10,2 > je .Lsysc_return > + ahi %r14,-__TASK_thread_struct # r14 now points to 'current' > lgf %r1,0(%r10,%r1) # load address of handler routine > lgr %r2,%r11 # pass pointer to pt_regs > basr %r14,%r1 # branch to interrupt-handler > > Because the 'basr' line relies on 'r14' having task_struct, I think? > > But I don't really know what I'm talking about here ... The basr instruction is one of the function calling instructions and %r14 is used for the return address. Between function calls the register is basically free. So far it is used for the task_struct pointer (the code following the "lg %r14,__TI_task(%r12)"). What I noticed is that the pointer is only used to access the embedded thread_struct. To get from the task_struct to a thread_struct a single aghi is needed. The rest is moving stuff around in asm-offsets.c -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
