From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267304AbUHWW3f (ORCPT ); Mon, 23 Aug 2004 18:29:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S268138AbUHWVh1 (ORCPT ); Mon, 23 Aug 2004 17:37:27 -0400 Received: from x35.xmailserver.org ([69.30.125.51]:51598 "EHLO x35.xmailserver.org") by vger.kernel.org with ESMTP id S267881AbUHWVYC (ORCPT ); Mon, 23 Aug 2004 17:24:02 -0400 X-AuthUser: davidel@xmailserver.org Date: Mon, 23 Aug 2004 14:23:35 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@bigblue.dev.mdolabs.com To: Linux Kernel Mailing List cc: Andy Kleen , Andrew Morton , Linus Torvalds Subject: [patch] lazy TSS's I/O bitmap copy ... Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org The following patch implements a lazy I/O bitmap copy for the i386 architecture. With I/O bitmaps now reaching considerable sizes, if the switched task does not perform any I/O operation, we can save the copy altogether. In my box X is working fine with the following patch, even if more test would be required. Signed-off-by: Davide Libenzi - Davide arch/i386/kernel/process.c | 33 +++++++++++---------------------- arch/i386/kernel/traps.c | 20 ++++++++++++++++++++ include/asm-i386/processor.h | 1 + 3 files changed, 32 insertions(+), 22 deletions(-) Index: arch/i386/kernel/process.c =================================================================== RCS file: /usr/src/bkcvs/linux-2.5/arch/i386/kernel/process.c,v retrieving revision 1.82 diff -u -r1.82 process.c --- a/arch/i386/kernel/process.c 14 Jul 2004 16:27:05 -0000 1.82 +++ b/arch/i386/kernel/process.c 23 Aug 2004 19:33:12 -0000 @@ -551,28 +551,17 @@ loaddebug(next, 7); } - if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr)) { - if (next->io_bitmap_ptr) { - /* - * 4 cachelines copy ... not good, but not that - * bad either. Anyone got something better? - * This only affects processes which use ioperm(). - * [Putting the TSSs into 4k-tlb mapped regions - * and playing VM tricks to switch the IO bitmap - * is not really acceptable.] - */ - memcpy(tss->io_bitmap, next->io_bitmap_ptr, - IO_BITMAP_BYTES); - tss->io_bitmap_base = IO_BITMAP_OFFSET; - } else - /* - * a bitmap offset pointing outside of the TSS limit - * causes a nicely controllable SIGSEGV if a process - * tries to use a port IO instruction. The first - * sys_ioperm() call sets up the bitmap properly. - */ - tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET; - } + /* + * Lazy TSS's I/O bitmap copy. We set an invalid offset here and + * we let the task to get a GPF in case an I/O instruction is performed. + * The handler of the GPF will verify that the faulting task has a valid + * I/O bitmap and, it true, does the real copy and restart the instruction. + * This will save us for redoundant copies when the currently switched task + * does not perform any I/O during its timeslice. + */ + tss->io_bitmap_base = next->io_bitmap_ptr ? INVALID_IO_BITMAP_OFFSET_LAZY: + INVALID_IO_BITMAP_OFFSET; + return prev_p; } Index: arch/i386/kernel/traps.c =================================================================== RCS file: /usr/src/bkcvs/linux-2.5/arch/i386/kernel/traps.c,v retrieving revision 1.77 diff -u -r1.77 traps.c --- a/arch/i386/kernel/traps.c 13 Jul 2004 18:02:33 -0000 1.77 +++ b/arch/i386/kernel/traps.c 23 Aug 2004 19:34:52 -0000 @@ -431,6 +431,26 @@ asmlinkage void do_general_protection(struct pt_regs * regs, long error_code) { + int cpu = smp_processor_id(); + struct tss_struct *tss = init_tss + cpu; + struct task_struct *tsk = current; + struct thread_struct *tsk_th = &tsk->thread; + + /* + * Perform the lazy TSS's I/O bitmap copy. If the TSS has an + * invalid offset set (the LAZY one) and the faulting thread has + * a valid I/O bitmap pointer, we copy the I/O bitmap in the TSS + * and we set the offset field correctly. Then we let the CPU to + * restart the faulting instruction. + */ + if (tss->io_bitmap_base == INVALID_IO_BITMAP_OFFSET_LAZY && + tsk_th->io_bitmap_ptr) { + memcpy(tss->io_bitmap, tsk_th->io_bitmap_ptr, + IO_BITMAP_BYTES); + tss->io_bitmap_base = IO_BITMAP_OFFSET; + return; + } + if (regs->eflags & X86_EFLAGS_IF) local_irq_enable(); Index: include/asm-i386/processor.h =================================================================== RCS file: /usr/src/bkcvs/linux-2.5/include/asm-i386/processor.h,v retrieving revision 1.68 diff -u -r1.68 processor.h --- a/include/asm-i386/processor.h 27 Jun 2004 17:53:48 -0000 1.68 +++ b/include/asm-i386/processor.h 23 Aug 2004 19:32:58 -0000 @@ -304,6 +304,7 @@ #define IO_BITMAP_LONGS (IO_BITMAP_BYTES/sizeof(long)) #define IO_BITMAP_OFFSET offsetof(struct tss_struct,io_bitmap) #define INVALID_IO_BITMAP_OFFSET 0x8000 +#define INVALID_IO_BITMAP_OFFSET_LAZY 0x9000 struct i387_fsave_struct { long cwd;