From d35ff22516b161f6d472f7f5371a89597b072d04 Mon Sep 17 00:00:00 2001 From: Michael Chang Date: Mon, 6 May 2024 10:34:22 +0800 Subject: [PATCH] net/drivers/ieee1275/ofnet: Remove 200 ms timeout in get_card_packet() to reduce input latency When GRUB image is netbooted on ppc64le, the keyboard input exhibits significant latency, reports even say that characters are processed about once per second. This issue makes interactively trying to debug a ppc64le config very difficult. It seems that the latency is largely caused by a 200 ms timeout in the idle event loop, during which the network card interface is consistently polled for incoming packets. Often, no packets arrive during this period, so the timeout nearly always expires, which blocks the response to key inputs. Furthermore, this 200 ms timeout might not need to be enforced at this basic layer, considering that GRUB performs synchronous reads and its timeout management is actually handled by higher layers, not directly in the card instance. Additionally, the idle polling, which reacts to unsolicited packets like ICMP and SLAAC, would be fine at a less frequent polling interval, rather than needing a timeout for receiving a response. For these reasons, we believe the timeout in get_card_packet() should be effectively removed. According to test results, the delay has disappeared, and it is now much easier to use interactively. Signed-Off-by: Michael Chang Tested-by: Tony Jones Reviewed-by: Daniel Kiper --- grub-core/net/drivers/ieee1275/ofnet.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/grub-core/net/drivers/ieee1275/ofnet.c b/grub-core/net/drivers/ieee1275/ofnet.c index 78f03df8e..3bf48b3f0 100644 --- a/grub-core/net/drivers/ieee1275/ofnet.c +++ b/grub-core/net/drivers/ieee1275/ofnet.c @@ -82,15 +82,11 @@ get_card_packet (struct grub_net_card *dev) grub_ssize_t actual; int rc; struct grub_ofnetcard_data *data = dev->data; - grub_uint64_t start_time; struct grub_net_buff *nb; - start_time = grub_get_time_ms (); - do - rc = grub_ieee1275_read (data->handle, dev->rcvbuf, dev->rcvbufsize, &actual); - while ((actual <= 0 || rc < 0) && (grub_get_time_ms () - start_time < 200)); + rc = grub_ieee1275_read (data->handle, dev->rcvbuf, dev->rcvbufsize, &actual); - if (actual <= 0) + if (actual <= 0 || rc < 0) return NULL; nb = grub_netbuff_alloc (actual + 2); -- 2.45.2