* [PATCH] ofnet: Remove 200 ms timeout in get_card_packet to reduce input latency
@ 2024-05-06 2:34 Michael Chang via Grub-devel
2024-05-27 4:03 ` Michael Chang via Grub-devel
2024-06-14 17:12 ` Daniel Kiper
0 siblings, 2 replies; 3+ messages in thread
From: Michael Chang via Grub-devel @ 2024-05-06 2:34 UTC (permalink / raw
To: The development of GNU GRUB; +Cc: Michael Chang, Tony Jones
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 <mchang@suse.com>
Tested-by: Tony Jones <tonyj@suse.com>
---
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);
--
2.44.0
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] ofnet: Remove 200 ms timeout in get_card_packet to reduce input latency
2024-05-06 2:34 [PATCH] ofnet: Remove 200 ms timeout in get_card_packet to reduce input latency Michael Chang via Grub-devel
@ 2024-05-27 4:03 ` Michael Chang via Grub-devel
2024-06-14 17:12 ` Daniel Kiper
1 sibling, 0 replies; 3+ messages in thread
From: Michael Chang via Grub-devel @ 2024-05-27 4:03 UTC (permalink / raw
To: The development of GNU GRUB; +Cc: Michael Chang, Tony Jones
Hi,
A gentle ping. With many patches posted these days, I hope this one is
not overlooked.
A quick note: This fixes a one second latency for each text input in the
grub interactive shell/editor when the image is net booted, as reported
on mkvterm on powerhmc, caused quite a few complaints from our internal
lab and QA.
Thanks,
Michael
On Mon, May 06, 2024 at 10:34:22AM GMT, Michael Chang wrote:
> 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 <mchang@suse.com>
> Tested-by: Tony Jones <tonyj@suse.com>
> ---
> 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);
> --
> 2.44.0
>
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] ofnet: Remove 200 ms timeout in get_card_packet to reduce input latency
2024-05-06 2:34 [PATCH] ofnet: Remove 200 ms timeout in get_card_packet to reduce input latency Michael Chang via Grub-devel
2024-05-27 4:03 ` Michael Chang via Grub-devel
@ 2024-06-14 17:12 ` Daniel Kiper
1 sibling, 0 replies; 3+ messages in thread
From: Daniel Kiper @ 2024-06-14 17:12 UTC (permalink / raw
To: Michael Chang; +Cc: grub-devel, Tony Jones
On Mon, May 06, 2024 at 10:34:22AM +0800, Michael Chang via Grub-devel wrote:
> 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 <mchang@suse.com>
> Tested-by: Tony Jones <tonyj@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Daniel
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2024-05-27 4:03 ` Michael Chang via Grub-devel
2024-06-14 17:12 ` Daniel Kiper
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