Re: [PATCH] remoteproc: core: Invoke subdev callbacks in list order
From: Bjorn Andersson <hidden>
Date: 2021-05-25 03:03:07
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linux-arm-msm, linux-remoteproc, lkml
On Mon 17 May 18:08 CDT 2021, Siddharth Gupta wrote:
Subdevices at the beginning of the subdev list should have higher priority than those at the end of the list. Reverse traversal of the list causes priority inversion, which can impact the performance of the device.
The subdev lists layers of the communication onion, we bring them up inside out and we take them down outside in. This stems from the primary idea that we want to be able to shut things down cleanly (in the case of a stop) and we pass the "crashed" flag to indicate to each recipient during "stop" that it may not rely on the response of a lower layer. As such, I don't think it's right to say that we have a priority inversion.
For example a device adds the glink, sysmon and ssr subdevs to its list. During a crash the ssr notification would go before the glink and sysmon notifications. This can cause a degraded response when a client driver waits for a response from the crashed rproc.
In general the design is such that components are not expected to communicate with the crashed remote when "crashed" is set, this avoids the single-remote crash. The case where this isn't holding up is when two remote processors crashes simultaneously, in which case e.g. sysmon has been seen hitting its timeout waiting for an ack from a dead remoteproc - but I was under the impression that this window shrunk dramatically as a side effect of us fixing the notification ordering.
quoted hunk
Signed-off-by: Siddharth Gupta <redacted> --- drivers/remoteproc/remoteproc_core.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-)diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c index 626a6b90f..ac8fc42 100644 --- a/drivers/remoteproc/remoteproc_core.c +++ b/drivers/remoteproc/remoteproc_core.c@@ -1167,7 +1167,7 @@ static int rproc_handle_resources(struct rproc *rproc, static int rproc_prepare_subdevices(struct rproc *rproc) { - struct rproc_subdev *subdev; + struct rproc_subdev *subdev, *itr; int ret; list_for_each_entry(subdev, &rproc->subdevs, node) {@@ -1181,9 +1181,11 @@ static int rproc_prepare_subdevices(struct rproc *rproc) return 0; unroll_preparation: - list_for_each_entry_continue_reverse(subdev, &rproc->subdevs, node) { - if (subdev->unprepare) - subdev->unprepare(subdev); + list_for_each_entry(itr, &rproc->subdevs, node) { + if (itr == subdev) + break; + if (itr->unprepare) + itr->unprepare(subdev); } return ret;@@ -1191,7 +1193,7 @@ static int rproc_prepare_subdevices(struct rproc *rproc) static int rproc_start_subdevices(struct rproc *rproc) { - struct rproc_subdev *subdev; + struct rproc_subdev *subdev, *itr; int ret; list_for_each_entry(subdev, &rproc->subdevs, node) {@@ -1205,9 +1207,11 @@ static int rproc_start_subdevices(struct rproc *rproc) return 0; unroll_registration: - list_for_each_entry_continue_reverse(subdev, &rproc->subdevs, node) { - if (subdev->stop) - subdev->stop(subdev, true); + list_for_each_entry(itr, &rproc->subdevs, node) { + if (itr == subdev) + break; + if (itr->stop) + itr->stop(itr, true); } return ret;@@ -1217,7 +1221,7 @@ static void rproc_stop_subdevices(struct rproc *rproc, bool crashed) { struct rproc_subdev *subdev; - list_for_each_entry_reverse(subdev, &rproc->subdevs, node) { + list_for_each_entry(subdev, &rproc->subdevs, node) {
I presume this is the case you actually care about, can you help me understand if you changed the others for consistence or if there's some flow of events where that might be necessary. Regards, Bjorn
quoted hunk
if (subdev->stop) subdev->stop(subdev, crashed); }@@ -1227,7 +1231,7 @@ static void rproc_unprepare_subdevices(struct rproc *rproc) { struct rproc_subdev *subdev; - list_for_each_entry_reverse(subdev, &rproc->subdevs, node) { + list_for_each_entry(subdev, &rproc->subdevs, node) { if (subdev->unprepare) subdev->unprepare(subdev); }-- Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
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