RE: [PATCH v4 2/2] pid: Remove pidhash

[Luck, Tony]

>ÂÂÂÂÂÂÂÂDEFINE(IA64_UPID_SHIFT, 5);
>
> Grepping for IA64_UPID_SHIFT leads us to some assembly
> code implementing fsys_getpid (why is that in assembly?!):

The fast system call path has a whole host of serious restrictions on what it can
touch. See Documentation/ia64/fsys.txt.  Why is getpid() a fast system call? I think
there was some application (or perhaps benchmark) that used it a lot.

>        add r8=IA64_PID_LEVEL_OFFSET,r17
>        ;;
>        ld4 r8=[r8]                             // r8 = pid->level
>        add r17=IA64_PID_UPID_OFFSET,r17        // r17 = &pid->numbers[0]
>        ;;
>        shl r8=r8,IA64_UPID_SHIFT
>        ;;
>        add r17=r17,r8                          // r17 = &pid->numbers[pid->level]
>        ;;
>        ld4 r8=[r17]                            // r8 = pid->numbers[pid->level].nr
>        ;;
>        mov r17=0
>
> Luckily it looks like this is only referencing the first members of struct upid,
> and you are removing the last member, so I suspect you will be fine changing the IA64
> to this:
>
>ÂÂÂÂÂÂÂÂBUILD_BUG_ON(sizeof(struct upid) != 16);
>ÂÂÂÂÂÂÂÂDEFINE(IA64_UPID_SHIFT, 4);
>
> Tony, does that look ok to you?

I think so.  Respin and Cc: me on both patches in the series and I'll take it for a spin
on h/w to make sure.

-Tony