From 972410b0232e97609fcefc8e408fe3037fcd607b Mon Sep 17 00:00:00 2001 From: Paolo 'Blaisorblade' Giarrusso Date: Fri, 31 Mar 2006 02:30:21 -0800 Subject: [PATCH] uml: clean arch_switch usage Call arch_switch also in switch_to_skas, even if it's, for now, a no-op for that case (and mark this in the comment); this will change soon. Also, arch_switch for TT mode is actually useless when the PT proxy (a complicate debugging instrumentation for TT mode) is not enabled. In fact, it only calls update_debugregs, which checks debugregs_seq against seq (to check if the registers are up-to-date - seq here means a "version number" of the registers). If the ptrace proxy is not enabled, debugregs_seq always stays 0 and update_debugregs will be a no-op. So, optimize this out (the compiler can't do it). Also, I've been disappointed by the fact that it would make a lot of sense if, after calling a successful update_debugregs(current->thread.arch.debugregs_seq), current->thread.arch.debugregs_seq were updated with the new debugregs_seq. But this is not done. Is this a bug or a feature? For all purposes, it seems a bug (otherwise the whole mechanism does not make sense, which is also a possibility to check), which causes some performance only problems (not correctness), since we write_debugregs when not needed. Also, as suggested by Jeff, remove a redundant enabling of SIGVTALRM, comprised in the subsequent local_irq_enable(). I'm just a bit dubious if ordering matters there... Signed-off-by: Paolo 'Blaisorblade' Giarrusso Acked-by: Jeff Dike Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/um/kernel/tt/process_kern.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'arch/um/kernel/tt') diff --git a/arch/um/kernel/tt/process_kern.c b/arch/um/kernel/tt/process_kern.c index 295c1ac817b..a9c1443fc54 100644 --- a/arch/um/kernel/tt/process_kern.c +++ b/arch/um/kernel/tt/process_kern.c @@ -51,6 +51,13 @@ void switch_to_tt(void *prev, void *next) c = 0; + /* Notice that here we "up" the semaphore on which "to" is waiting, and + * below (the read) we wait on this semaphore (which is implemented by + * switch_pipe) and go sleeping. Thus, after that, we have resumed in + * "to", and can't use any more the value of "from" (which is outdated), + * nor the value in "to" (since it was the task which stole us the CPU, + * which we don't care about). */ + err = os_write_file(to->thread.mode.tt.switch_pipe[1], &c, sizeof(c)); if(err != sizeof(c)) panic("write of switch_pipe failed, err = %d", -err); @@ -77,7 +84,7 @@ void switch_to_tt(void *prev, void *next) change_sig(SIGALRM, alrm); change_sig(SIGPROF, prof); - arch_switch(); + arch_switch_to_tt(prev_sched, current); flush_tlb_all(); local_irq_restore(flags); @@ -141,7 +148,6 @@ static void new_thread_handler(int sig) set_cmdline("(kernel thread)"); change_sig(SIGUSR1, 1); - change_sig(SIGVTALRM, 1); change_sig(SIGPROF, 1); local_irq_enable(); if(!run_kernel_thread(fn, arg, ¤t->thread.exec_buf)) -- cgit v1.2.3-70-g09d2