dmesg 的基本使用
网上的各种回答基本都是误导的， https://stackoverflow.com/questions/28936199/why-is-pr-debug-of-the-linux-kernel-not-giving-any-output 只需要看这两个 kernel 的文档就可以了
- https://www.kernel.org/doc/html/latest/core-api/printk-basics.html
- https://www.kernel.org/doc/html/latest/admin-guide/dynamic-debug-howto.html
- https://www.kernel.org/doc/html/latest/core-api/printk-formats.html
printk 是 console level 而不是 dmesg 中控制的 level
文档中说明的是:
cat /proc/sys/kernel/printk
4 4 1 7
The result shows the current, default, minimum and boot-time-default log levels.
只有在 console 中展示的 dmesg : echo 8 | sudo tee /proc/sys/kernel/printk 可以，那么 KERN_DEBUG 才可以展示
printk(KERN_DEBUG "[[printk debug]]\n");
[ 194.027022] [[printk debug]]
而 dmesg 中，这个输出总是有的。也就是 dmesg 中的输出根本不受 /proc/sys/kernel/printk 的影响， 总是有的。dmesg 只会收到 dynamic_debug 的影响
而 console 会同时受到 dynamic_debug 和 /proc/sys/kernel/printk 的影响
配置一下启动参数
loglevel= [KNL,EARLY]
All Kernel Messages with a loglevel smaller than the
console loglevel will be printed to the console. It can
also be changed with klogd or other programs. The
loglevels are defined as follows:
0 (KERN_EMERG) system is unusable
1 (KERN_ALERT) action must be taken immediately
2 (KERN_CRIT) critical conditions
3 (KERN_ERR) error conditions
4 (KERN_WARNING) warning conditions
5 (KERN_NOTICE) normal but significant condition
6 (KERN_INFO) informational
7 (KERN_DEBUG) debug-level messages
log_buf_len=n[KMG] [KNL,EARLY]
Sets the size of the printk ring buffer, in bytes.
n must be a power of two and greater than the
minimal size. The minimal size is defined by
LOG_BUF_SHIFT kernel config parameter. There
is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config
parameter that allows to increase the default size
depending on the number of CPUs. See init/Kconfig
for more details.
以为可以影响 /proc/sys/kernel/printk ，但是其实并不可以的。
这里几个参数是做什么的
/sys/module/printk/parameters
在这里有两个函数: kernel/printk/sysctl.c
类似这里的调试接口，什么时候可以打开?
dev_dbg
*/
static void virtscsi_complete_cmd(struct virtio_scsi *vscsi, void *buf)
{
struct virtio_scsi_cmd *cmd = buf;
struct scsi_cmnd *sc = cmd->sc;
struct virtio_scsi_cmd_resp *resp = &cmd->resp.cmd;
struct virtio_scsi_target_state *tgt =
scsi_target(sc->device)->hostdata;
dev_dbg(&sc->device->sdev_gendev,
"cmd %p response %u status %#02x sense_len %u\n",
sc, resp->response, resp->status, resp->sense_len);
dynamic_debug
支持 module 加载时和内核启动的时候配置
其他细节在 code/trace/dynamic.sh 中
- /proc/dynamic_debug/control 和 /sys/kernel/debug/dynamic_debug/control 是什么关系
这个东西是做什么的
include/net/net_debug.h 中偶然发现了这个东西
#if defined(CONFIG_DYNAMIC_DEBUG) || \
(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
#define netif_dbg(priv, type, netdev, format, args...) \
do { \
if (netif_msg_##type(priv)) \
dynamic_netdev_dbg(netdev, format, ##args); \
} while (0)
对于是对于 dynamic_debug 机制再添加了一些功能？
先将 man dmesg(1) 都看一遍吧
sudo sysctl -w kernel.printk=4 sudo sysctl kernel.printk
CONSOLE_LOGLEVEL_DEFAULT 做什么的?
总结下常见的使用技巧吧
再次，理解下 printk 的输出结果
quiet [KNL] Disable most log messages
为什么实时性和 printk 的关系这么大
太复杂了
- https://lwn.net/Articles/800946/
- https://lpc.events/event/4/contributions/290/attachments/276/463/lpc2019_jogness_printk.pdf
如果想让启动的时候的 pr_debug 打开如何
pr_debug("v" INTEL_IDLE_VERSION " model 0x%X\n",
boot_cpu_data.x86_model);
总结不错: https://www.cnblogs.com/pengdonglin137/p/5808373.html
有趣的调查
https://spectrum.library.concordia.ca/id/eprint/987184/1/Patel_MSc_F2020.pdf
这里总结了 options
- Documentation/admin-guide/sysctl/kernel.rst
cat /proc/sys/kernel/printk_delay cat /proc/sys/kernel/printk_ratelimit : 在多长的时间里面 cat /proc/sys/kernel/printk_ratelimit_burst : 最多打印多少的信息出来
原来还可以这样啊
sudo dmesg --level=err,warn
如何把特定模块的日志屏蔽掉
例如 13900k 的行为:
[263498.057599] wlo1: disconnect from AP 20:ab:48:6c:8b:50 for new auth to 20:ab:48:6c:89:b0
[263498.099938] wlo1: authenticate with 20:ab:48:6c:89:b0 (local address=70:a8:d3:66:73:bc)
[263498.100769] wlo1: send auth to 20:ab:48:6c:89:b0 (try 1/3)
[263498.127029] wlo1: authenticated
[263498.127203] wlo1: associate with 20:ab:48:6c:89:b0 (try 1/3)
[263498.131187] wlo1: RX ReassocResp from 20:ab:48:6c:89:b0 (capab=0x1511 status=0 aid=7)
[263498.135735] wlo1: associated
[263498.167059] wlo1: Limiting TX power to 20 (23 - 3) dBm as advertised by 20:ab:48:6c:89:b0
[263531.932636] wlo1: disconnect from AP 20:ab:48:6c:89:b0 for new auth to 20:ab:48:6c:8b:50
[263531.974011] wlo1: authenticate with 20:ab:48:6c:8b:50 (local address=70:a8:d3:66:73:bc)
[263531.974832] wlo1: send auth to 20:ab:48:6c:8b:50 (try 1/3)
[263532.001477] wlo1: authenticated
[263532.002142] wlo1: associate with 20:ab:48:6c:8b:50 (try 1/3)
[263532.006334] wlo1: RX ReassocResp from 20:ab:48:6c:8b:50 (capab=0x1511 status=0 aid=3)
[263532.010993] wlo1: associated
[263532.018538] wlo1: Limiting TX power to 30 (33 - 3) dBm as advertised by 20:ab:48:6c:8b:50
[264123.191197] iwlwifi 0000:00:14.3: missed beacons exceeds threshold, but receiving data. Stay connected, Expect bugs.
[264123.191201] iwlwifi 0000:00:14.3: missed_beacons:19, missed_beacons_since_rx:1
[264123.293593] iwlwifi 0000:00:14.3: missed beacons exceeds threshold, but receiving data. Stay connected, Expect bugs.
[264123.293597] iwlwifi 0000:00:14.3: missed_beacons:20, missed_beacons_since_rx:1
[264123.396005] iwlwifi 0000:00:14.3: missed beacons exceeds threshold, but receiving data. Stay connected, Expect bugs.
[264123.396008] iwlwifi 0000:00:14.3: missed_beacons:21, missed_beacons_since_rx:1
[264123.498404] iwlwifi 0000:00:14.3: missed beacons exceeds threshold, but receiving data. Stay connected, Expect bugs.
[264123.498407] iwlwifi 0000:00:14.3: missed_beacons:22, missed_beacons_since_rx:1
[264123.600783] iwlwifi 0000:00:14.3: missed beacons exceeds threshold, but receiving data. Stay connected, Expect bugs.
[264123.600785] iwlwifi 0000:00:14.3: missed_beacons:23, missed_beacons_since_rx:1
[264123.703194] iwlwifi 0000:00:14.3: missed beacons exceeds threshold, but receiving data. Stay connected, Expect bugs.
似乎这些日志很难去掉发
demsg -n 4 可以屏蔽 pr_info 日志
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