Messages in this thread Patch in this message | | | Date | Mon, 3 Jul 2006 02:49:48 -0700 | From | Stephane Eranian <> | Subject | Re: [PATCH 10/17] 2.6.17.1 perfmon2 patch for review: PMU context switch |
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Andi,
Here is a first cut at the patch to simplify the context switch for the common case and also touch 2 cachelines (instead of 3). There are 2 new TIF flags. I just tried this on x86_64 but I believe we could do the same on i386.
Is that what you were thinking about?
Thanks
On Fri, Jun 30, 2006 at 02:59:05PM +0200, Andi Kleen wrote: > Stephane Eranian <eranian@hpl.hp.com> writes: > > > Andi, > > > > Thanks for your feedback. I will make the changes you > > requested. > > > > About the context switch code, what about I do the following > > in __switch_to(): > > > > __kprobes struct task_struct * > > __switch_to(struct task_struct *prev_p, struct task_struct *next_p) > > { > > struct thread_struct *prev = &prev_p->thread, > > *next = &next_p->thread; > > int cpu = smp_processor_id(); > > struct tss_struct *tss = &per_cpu(init_tss, cpu); > > > > if (unlikely(__get_cpu_var(pmu_ctx) || next_p->pfm_context)) > > __pfm_ctxswout(prev_p, next_p); > > > > /* > > * Reload esp0, LDT and the page table pointer: > > */ > > tss->rsp0 = next->rsp0; > > > > There is now a single hook and a conditional branch. > > this is similar to what you have with the debug registers. > > It's still more than there was before. Also __get_cpu_var > is quite a lot of instructions. > > I would suggest you borrow some bits in one of the process > or thread info flags and then do a single test > > if (unlikely(thr->flags & (DEBUG|PERFMON)) != 0) { > if (flags & DEBUG) > ... do debug ... > if (flags & PERFMON) > ... do perfmon ... > } > > [which you're at it you can probably add ioports in there too - > improving existing code is always a good thing] > > Ideally flags is in some cache line that is already > touched during context switch. If not you might need > to change the layout. > > It's ok to put the do_perfmon stuff into a separate noinline > function because that will disturb the register allocation > in the caller less. > > I would suggest doing this in separate preparing patches that > first just do it for existing facilities. > > -Andi > > P.S.: My comments probably apply to the i386 versions too > although I haven't read them.
--
-Stephane diff -urNp linux-2.6.17.2.orig/arch/x86_64/ia32/ptrace32.c linux-2.6.17.2-tif/arch/x86_64/ia32/ptrace32.c --- linux-2.6.17.2.orig/arch/x86_64/ia32/ptrace32.c 2006-06-17 18:49:35.000000000 -0700 +++ linux-2.6.17.2-tif/arch/x86_64/ia32/ptrace32.c 2006-06-30 09:02:16.000000000 -0700 @@ -118,6 +118,10 @@ static int putreg32(struct task_struct * if ((0x5454 >> ((val >> (16 + 4*i)) & 0xf)) & 1) return -EIO; child->thread.debugreg7 = val; + if (val) + set_tsk_thread_flag(child, TIF_DEBUG); + else + clear_tsk_thread_flag(child, TIF_DEBUG); break; default: diff -urNp linux-2.6.17.2.orig/arch/x86_64/kernel/ioport.c linux-2.6.17.2-tif/arch/x86_64/kernel/ioport.c --- linux-2.6.17.2.orig/arch/x86_64/kernel/ioport.c 2006-06-17 18:49:35.000000000 -0700 +++ linux-2.6.17.2-tif/arch/x86_64/kernel/ioport.c 2006-07-03 02:06:59.000000000 -0700 @@ -56,6 +56,7 @@ asmlinkage long sys_ioperm(unsigned long memset(bitmap, 0xff, IO_BITMAP_BYTES); t->io_bitmap_ptr = bitmap; + set_thread_flag(TIF_IO_BITMAP); } /* diff -urNp linux-2.6.17.2.orig/arch/x86_64/kernel/process.c linux-2.6.17.2-tif/arch/x86_64/kernel/process.c --- linux-2.6.17.2.orig/arch/x86_64/kernel/process.c 2006-06-17 18:49:35.000000000 -0700 +++ linux-2.6.17.2-tif/arch/x86_64/kernel/process.c 2006-07-03 02:35:25.000000000 -0700 @@ -356,6 +356,7 @@ void exit_thread(void) */ memset(tss->io_bitmap, 0xff, t->io_bitmap_max); t->io_bitmap_max = 0; + clear_thread_flag(TIF_IO_BITMAP); put_cpu(); } } @@ -366,7 +367,7 @@ void flush_thread(void) struct thread_info *t = current_thread_info(); if (t->flags & _TIF_ABI_PENDING) - t->flags ^= (_TIF_ABI_PENDING | _TIF_IA32); + t->flags ^= (_TIF_ABI_PENDING | _TIF_IA32 | _TIF_DEBUG); tsk->thread.debugreg0 = 0; tsk->thread.debugreg1 = 0; @@ -459,7 +460,7 @@ int copy_thread(int nr, unsigned long cl asm("mov %%es,%0" : "=m" (p->thread.es)); asm("mov %%ds,%0" : "=m" (p->thread.ds)); - if (unlikely(me->thread.io_bitmap_ptr != NULL)) { + if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) { p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL); if (!p->thread.io_bitmap_ptr) { p->thread.io_bitmap_max = 0; @@ -467,6 +468,7 @@ int copy_thread(int nr, unsigned long cl } memcpy(p->thread.io_bitmap_ptr, me->thread.io_bitmap_ptr, IO_BITMAP_BYTES); + set_tsk_thread_flag(p, TIF_IO_BITMAP); } /* @@ -484,7 +486,7 @@ int copy_thread(int nr, unsigned long cl } err = 0; out: - if (err && p->thread.io_bitmap_ptr) { + if (err && test_tsk_thread_flag(p, TIF_IO_BITMAP)) { kfree(p->thread.io_bitmap_ptr); p->thread.io_bitmap_max = 0; } @@ -584,38 +586,34 @@ __switch_to(struct task_struct *prev_p, task_stack_page(next_p) + THREAD_SIZE - PDA_STACKOFFSET); /* - * Now maybe reload the debug registers + * Now maybe reload the debug registers and handle I/O bitmaps */ - if (unlikely(next->debugreg7)) { - loaddebug(next, 0); - loaddebug(next, 1); - loaddebug(next, 2); - loaddebug(next, 3); - /* no 4 and 5 */ - loaddebug(next, 6); - loaddebug(next, 7); - } - + if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW)) + || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) { - /* - * Handle the IO bitmap - */ - if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr)) { - if (next->io_bitmap_ptr) + if (test_tsk_thread_flag(next_p, TIF_DEBUG)) { + loaddebug(next, 0); + loaddebug(next, 1); + loaddebug(next, 2); + loaddebug(next, 3); + /* no 4 and 5 */ + loaddebug(next, 6); + loaddebug(next, 7); + } + if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) { /* * Copy the relevant range of the IO bitmap. * Normally this is 128 bytes or less: */ memcpy(tss->io_bitmap, next->io_bitmap_ptr, - max(prev->io_bitmap_max, next->io_bitmap_max)); - else { + max(prev->io_bitmap_max, next->io_bitmap_max)); + } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) { /* * Clear any possible leftover bits: */ memset(tss->io_bitmap, 0xff, prev->io_bitmap_max); } } - return prev_p; } diff -urNp linux-2.6.17.2.orig/arch/x86_64/kernel/ptrace.c linux-2.6.17.2-tif/arch/x86_64/kernel/ptrace.c --- linux-2.6.17.2.orig/arch/x86_64/kernel/ptrace.c 2006-06-17 18:49:35.000000000 -0700 +++ linux-2.6.17.2-tif/arch/x86_64/kernel/ptrace.c 2006-06-30 09:30:57.000000000 -0700 @@ -420,9 +420,16 @@ long arch_ptrace(struct task_struct *chi if ((0x5554 >> ((data >> (16 + 4*i)) & 0xf)) & 1) break; if (i == 4) { - child->thread.debugreg7 = data; + child->thread.debugreg7 = data; + if (data) { + pr_info("set TIF_DEBUG for [%d]\n", child->pid); + set_tsk_thread_flag(child, TIF_DEBUG); + } else { + pr_info("clear TIF_DEBUG for [%d]\n", child->pid); + clear_tsk_thread_flag(child, TIF_DEBUG); + } ret = 0; - } + } break; } break; diff -urNp linux-2.6.17.2.orig/include/asm-x86_64/thread_info.h linux-2.6.17.2-tif/include/asm-x86_64/thread_info.h --- linux-2.6.17.2.orig/include/asm-x86_64/thread_info.h 2006-06-17 18:49:35.000000000 -0700 +++ linux-2.6.17.2-tif/include/asm-x86_64/thread_info.h 2006-07-03 02:32:25.000000000 -0700 @@ -106,6 +106,8 @@ static inline struct thread_info *stack_ #define TIF_FORK 18 /* ret_from_fork */ #define TIF_ABI_PENDING 19 #define TIF_MEMDIE 20 +#define TIF_DEBUG 21 /* uses debug registers */ +#define TIF_IO_BITMAP 22 /* uses I/O bitmap */ #define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE) #define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME) @@ -119,6 +121,8 @@ static inline struct thread_info *stack_ #define _TIF_IA32 (1<<TIF_IA32) #define _TIF_FORK (1<<TIF_FORK) #define _TIF_ABI_PENDING (1<<TIF_ABI_PENDING) +#define _TIF_DEBUG (1<<TIF_DEBUG) +#define _TIF_IO_BITMAP (1<<TIF_IO_BITMAP) /* work to do on interrupt/exception return */ #define _TIF_WORK_MASK \ @@ -126,6 +130,9 @@ static inline struct thread_info *stack_ /* work to do on any return to user space */ #define _TIF_ALLWORK_MASK (0x0000FFFF & ~_TIF_SECCOMP) +/* flags to check in __switch_to() */ +#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP) + #define PREEMPT_ACTIVE 0x10000000 /* | |