diff options
author | Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> | 2006-03-31 02:30:21 -0800 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-03-31 12:18:52 -0800 |
commit | 972410b0232e97609fcefc8e408fe3037fcd607b (patch) | |
tree | 2de18ed5d823dc7e24c0171f720f6354a9cd57e4 /arch/um/kernel/tt/process_kern.c | |
parent | fbdf2161552a2065047e5df2dbf9ebf69d66a0e9 (diff) |
[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 <blaisorblade@yahoo.it>
Acked-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch/um/kernel/tt/process_kern.c')
-rw-r--r-- | arch/um/kernel/tt/process_kern.c | 10 |
1 files changed, 8 insertions, 2 deletions
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)) |