On 2011-02-01 17:53, Anthony Liguori wrote:
> On 02/01/2011 10:36 AM, Jan Kiszka wrote:
>> On 2011-02-01 16:54, Chris Wright wrote:
>>
>>> KVM upstream merge: status, plans, coordination
>>> - Jan has a git tree, consolidating
>>> - qemu-kvm io threading is still an issue
>>> - Anthony wants to just merge
>>> - concerns with non-x86 arch and merge
>>> - concerns with big-bang patch merge and following stability
>>> - post 0.14 conversion to glib mainloop, non-upstreamed qemu-kvm will be
>>> a problem if it's not there by then
>>> - testing and nuances are still an issue (e.g. stefan berger's mmio read issue)
>>> - qemu-kvm still evolving, needs to get sync'd or it will keep diverging
>>> - 2 implementations of main init, cpu init, Jan has merged them into one
>>> - qemu-kvm-x86.c file that's only a few hundred lines
>>> - review as one patch to see the fundamental difference
>>>
>> More precisely, my current work flow is to pick some function(s), e.g.
>> kvm_cpu_exec/kvm_run, and start wondering "What needs to be done to
>> upstream so that qemu-kvm could use that implementation?". If they
>> differ, the reasons need to be understood and patched away, either by
>> fixing/enhancing upstream or simplifying qemu-kvm. Once the upstream
>> changes are merged back, a qemu-kvm patch is posted to switch to that
>> version.
>>
>> Any help will be welcome, either via review of my subtle regressions or
>> on resolving concrete differences.
>>
>> E.g. posix-aio-compat.c: Why does qemu-kvm differ here? If it's because
>> of its own iothread code, can we wrap that away or do we need to
>> consolidate the threading code first? Or do we need to fix something in
>> upstream?
>>
>
> I bet it's the eventfd thing. It's arbitrary. If you've got a small
> diff post your series, I'd be happy to take a look at it and see what I
> can explain.
>
Looks like it's around signalfd and its emulation:
[git diff qemu/master..master posix-aio-compat.c]
diff --git a/posix-aio-compat.c b/posix-aio-compat.c
index fa5494d..0704064 100644
--- a/posix-aio-compat.c
+++ b/posix-aio-compat.c
@@ -28,6 +28,7 @@
#include "qemu-common.h"
#include "trace.h"
#include "block_int.h"
+#include "compatfd.h"
#include "block/raw-posix-aio.h"
@@ -55,7 +56,7 @@ struct qemu_paiocb {
};
typedef struct PosixAioState {
- int rfd, wfd;
+ int fd;
struct qemu_paiocb *first_aio;
} PosixAioState;
@@ -474,18 +475,29 @@ static int posix_aio_process_queue(void *opaque)
static void posix_aio_read(void *opaque)
{
PosixAioState *s = opaque;
- ssize_t len;
+ union {
+ struct qemu_signalfd_siginfo siginfo;
+ char buf[128];
+ } sig;
+ size_t offset;
- /* read all bytes from signal pipe */
- for (;;) {
- char bytes[16];
+ /* try to read from signalfd, don't freak out if we can't read anything */
+ offset = 0;
+ while (offset < 128) {
+ ssize_t len;
- len = read(s->rfd, bytes, sizeof(bytes));
+ len = read(s->fd, sig.buf + offset, 128 - offset);
if (len == -1 && errno == EINTR)
- continue; /* try again */
- if (len == sizeof(bytes))
- continue; /* more to read */
- break;
+ continue;
+ if (len == -1 && errno == EAGAIN) {
+ /* there is no natural reason for this to happen,
+ * so we'll spin hard until we get everything just
+ * to be on the safe side. */
+ if (offset > 0)
+ continue;
+ }
+
+ offset += len;
}
posix_aio_process_queue(s);
@@ -499,20 +511,6 @@ static int posix_aio_flush(void *opaque)
static PosixAioState *posix_aio_state;
-static void aio_signal_handler(int signum)
-{
- if (posix_aio_state) {
- char byte = 0;
- ssize_t ret;
-
- ret = write(posix_aio_state->wfd, &byte, sizeof(byte));
- if (ret < 0 && errno != EAGAIN)
- die("write()");
- }
-
- qemu_service_io();
-}
-
static void paio_remove(struct qemu_paiocb *acb)
{
struct qemu_paiocb **pacb;
@@ -616,9 +614,8 @@ BlockDriverAIOCB *paio_ioctl(BlockDriverState *bs, int fd,
int paio_init(void)
{
- struct sigaction act;
+ sigset_t mask;
PosixAioState *s;
- int fds[2];
int ret;
if (posix_aio_state)
@@ -626,24 +623,21 @@ int paio_init(void)
s = qemu_malloc(sizeof(PosixAioState));
- sigfillset(&act.sa_mask);
- act.sa_flags = 0; /* do not restart syscalls to interrupt select() */
- act.sa_handler = aio_signal_handler;
- sigaction(SIGUSR2, &act, NULL);
+ /* Make sure to block AIO signal */
+ sigemptyset(&mask);
+ sigaddset(&mask, SIGUSR2);
+ sigprocmask(SIG_BLOCK, &mask, NULL);
s->first_aio = NULL;
- if (qemu_pipe(fds) == -1) {
- fprintf(stderr, "failed to create pipe\n");
+ s->fd = qemu_signalfd(&mask);
+ if (s->fd == -1) {
+ fprintf(stderr, "failed to create signalfd\n");
return -1;
}
- s->rfd = fds[0];
- s->wfd = fds[1];
-
- fcntl(s->rfd, F_SETFL, O_NONBLOCK);
- fcntl(s->wfd, F_SETFL, O_NONBLOCK);
+ fcntl(s->fd, F_SETFL, O_NONBLOCK);
- qemu_aio_set_fd_handler(s->rfd, posix_aio_read, NULL, posix_aio_flush,
+ qemu_aio_set_fd_handler(s->fd, posix_aio_read, NULL, posix_aio_flush,
posix_aio_process_queue, s);
ret = pthread_attr_init(&attr);
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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