From: Michael Ellerman Date: Wed, 7 Jun 2006 07:10:03 +0000 (+1000) Subject: [PATCH] powerpc: Make rtas console _much_ faster X-Git-Tag: firefly_0821_release~35458^2~225^2~66 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=b53744612f276ad20c5d7ef33ac991ec13101417;p=firefly-linux-kernel-4.4.55.git [PATCH] powerpc: Make rtas console _much_ faster Currently the hvc_rtas driver is painfully slow to use. Our "benchmark" is ls -R /etc, which spits out about 27866 characters. The theoretical maximum speed would be about 2.2 seconds, the current code takes ~50 seconds. The core of the problem is that sometimes when the tty layer asks us to push characters the firmware isn't able to handle some or all of them, and so returns an error. The current code sees this and just returns to the tty code with the buffer half sent. The khvcd thread will eventually wake up and try to push more characters, which will usually work because by then the firmware's had time to make room. But the khvcd thread only wakes up every 10 milliseconds, which isn't fast enough. So change the khvcd thread logic so that if there's an incomplete write we yield() and then immediately try writing again. Doing so makes POLL_QUICK and POLL_WRITE synonymous, so remove POLL_QUICK. With this patch our "benchmark" takes ~2.8 seconds. Signed-off-by: Michael Ellerman Signed-off-by: Paul Mackerras --- diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c index 2b6a56b2bf35..a5c6a9d7ff08 100644 --- a/drivers/char/hvc_console.c +++ b/drivers/char/hvc_console.c @@ -553,7 +553,6 @@ static int hvc_chars_in_buffer(struct tty_struct *tty) #define HVC_POLL_READ 0x00000001 #define HVC_POLL_WRITE 0x00000002 -#define HVC_POLL_QUICK 0x00000004 static int hvc_poll(struct hvc_struct *hp) { @@ -568,6 +567,7 @@ static int hvc_poll(struct hvc_struct *hp) /* Push pending writes */ if (hp->n_outbuf > 0) hvc_push(hp); + /* Reschedule us if still some write pending */ if (hp->n_outbuf > 0) poll_mask |= HVC_POLL_WRITE; @@ -680,7 +680,7 @@ int khvcd(void *unused) poll_mask |= HVC_POLL_READ; if (hvc_kicked) continue; - if (poll_mask & HVC_POLL_QUICK) { + if (poll_mask & HVC_POLL_WRITE) { yield(); continue; }