November 2020 - kernelnewbies@kernelnewbies.org

Re: Scheduler benchmarks
by Muni Sekhar April 29, 2021

April 29, 2021

On Tue, Aug 18, 2020 at 11:45 PM peter enderborg <peter.enderborg(a)sony.com> wrote: > > On 8/18/20 7:53 PM, Muni Sekhar wrote: > > On Tue, Aug 18, 2020 at 11:06 PM Greg KH <greg(a)kroah.com> wrote: > >> On Tue, Aug 18, 2020 at 11:01:35PM +0530, Muni Sekhar wrote: > >>> On Tue, Aug 18, 2020 at 10:44 PM Greg KH <greg(a)kroah.com> wrote: > >>>> On Tue, Aug 18, 2020 at 10:24:13PM +0530, Muni Sekhar wrote: > >>>>> On Tue, Aug 18, 2020 at 8:06 PM Greg KH <greg(a)kroah.com> wrote: > >>>>>> On Tue, Aug 18, 2020 at 08:00:11PM +0530, Muni Sekhar wrote: > >>>>>>> Hi all, > >>>>>>> > >>>>>>> I’ve two identical Linux systems with only kernel differences. > >>>>>> What are the differences in the kernels? > >>>> You didn't answer this question, is this the same kernel source being > >>>> compared here? Same version? Same compiler? Everything identical? > >>> Both systems are having exactly the same hardware configuration. > >>> Compiler and kernel versions are different. One system has Ubuntu > >>> 16.04.4 LTS(4.4.0-66-generic kernel with gcc version 5.4.0) kernel and > >>> the other one has Ubuntu 18.04.4 LTS(4.15.0-91-generic kernel with gcc > >>> version 7.5.0). > >> Those are _very_ different kernel versions, with many years and tens of > >> thousands of different changes between them. > >> > >> Hopefully the newer kernel is faster, so just stick with that :) > > But unfortunately the newer kernel is very slow, that is the reason > > for starting this investigation :) > > Any type of help, and guidelines to dive deeper will be highly appreciated. > > On the 4.4 kernel you dont have > > +CONFIG_RETPOLINE=y > +CONFIG_INTEL_RDT=y Thanks! That is helpful. Yes, I see 4.4 kernel don't have the above two config options. What analysis can be done to narrow down the root cause? Any example of reference could be helpful to understand. > > And your base is very different two. > > Try to use mainline on both system and see. > > You can also use the same base kernel version from ubuntu and > > run your test. > > > >> greg k-h > > > > > -- Thanks, Sekhar

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Setting group/other write flags not honoured in open
by Nicky Chorley Jan. 8, 2021

Jan. 8, 2021

Hi folks, I hope it's OK to ask this question here. I'm reading The Linux Programming Interface and am beginning to get to grips with the file oriented system calls. I have a program that calls open to create a file, specifying the mode flags for owner, group, other read and write. The file is created sucessfully, but when I look at its permissions, I only see the read perms set for group and others: > ./create_file foo > ls -l foo -rw-r--r-- 1 nick users 0 Oct 31 14:52 foo Why would that be? The entirety of my program is #include <fcntl.h> #include <unistd.h> int main(int argc, char *argv[]) { int open_flags = O_CREAT | O_WRONLY | O_TRUNC; mode_t file_perms = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH; int output_fd = open(argv[1], open_flags, file_perms); close(output_fd); } I also ran the program with strace and the perms in the openat call are as I would expect: openat(AT_FDCWD, "foo", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3 I don't understand why the group and other write flags aren't being set. Could someone help shed some light on this please? I'm not sure what factors influence this, but I'm running openSUSE Leap 15.2, with kernel 5.3.18-lp152.47-default, gcc 7.5.0 and glibc 2.26. Thanks, Nicky

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question about arm64 __primary_switched code
by ckim＠etri.re.kr Nov. 30, 2020

Nov. 30, 2020

Hello, I have put a question on stackoverflow but nobody answers there yet. I'll grateful if someone gives me some comments or answers. (it's about understanding arm64 assembly code) https://stackoverflow.com/questions/65051120/understanding-arm64-assembly-ad r-l-ldr-l-str-l-in-a-linux-kernel-code?noredirect=1#comment115012976_6505112 0 Thank you. Chan

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es8316 i2c-ESSX8316:00: ASoC: error at soc_component_write_no_lock
by Jeffrey Walton Nov. 20, 2020

Nov. 20, 2020

Hi Everyone, Attached is a dmesg for a Fedora 33 machine that went sideways tonight after a 'dnf upgrade' and reboot. The machine is a low-end Cherry Trail. It boots but something broke with the USB modem. The error message is " Failed to open device /dev/ttyACM0: No such file or directory". The dmesg is full of: [ 14.970968] es8316 i2c-ESSX8316:00: ASoC: error at soc_component_write_no_lock on i2c-ESSX8316:00: -121 [ 14.976669] es8316 i2c-ESSX8316:00: ASoC: error at soc_component_write_no_lock on i2c-ESSX8316:00: -121 [ 15.008046] es8316 i2c-ESSX8316:00: ASoC: error at soc_component_write_no_lock on i2c-ESSX8316:00: -121 [ 15.008166] es8316 i2c-ESSX8316:00: ASoC: error at soc_component_write_no_lock on i2c-ESSX8316:00: -121 What kernel component should this bug report be filed against? Thanks in advance.

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toolchain name for building linux kernel?
by ckim＠etri.re.kr Nov. 19, 2020

Nov. 19, 2020

Hi, Some years ago, I used to use sparc-ab-elf- to build linux kernel. I thought that tool was for building bare-metal program. (because linux kernel is a kind of bare-metal program itself) We had also sparc-ab-linux- that were used for compiling application that runs on linux. Recently, I found a website that I should use aarch64-linux-gnu tool to build the kernel. I tried following it and it generated vmlinux file. (I can't find the web page link, but I'm sure I wrote that procedure down when I built vmlinux) Now I find it strange, because the tool name 'aarch64-linux-gnu-' seems to be the one for compiling application on linux! Am I missing something? Could anyone clarify what is wrong with my idea? Chan

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power management
by Pankaj Joshi Nov. 18, 2020

Nov. 18, 2020

Hi, I am working on BBB AM335x for power management stuff as i am very new to linux power management i need a bit help i am trying to achieve following using sysfs but i didnt got sucess i want to put my whole system into sleep state /idle state except WiFi and backlight, when i am writting* $echo mem > /sys/power/state* my whole system is going into sleep state similarly i have checked with */sys/class/backlight *but didnt worth. Can someone help me how i can do it ? How i can suspend and resume particular device only ?? Thanks

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arm64: Question about barriers with the mmu off
by Wonhyuk Yang Nov. 18, 2020

Nov. 18, 2020

Hi, I have a question about dmb barriers in arm64's head.S. In the head.S, I could see the pattern below several times. str w0, [x1] dmb sys dc ivac, x1 // Invalidate potentially stale cache line I found that, Commit(fix cache flushing and barriers in set_cpu_boot_mode_flag) explained the code. > This patch reworks the broken flushing code so that we: > > (1) Use a DMB to order the strongly-ordered write of the cacheline > against the subsequent cache-maintenance operation (by-VA > operations only hazard against normal, cacheable accesses). > > (2) Use a single dc ivac instruction to invalidate any clean lines > containing a stale copy of the line after it has been updated. > Use a DMB to order the strongly-> ordered write of the cacheline But I can't understand why the store operation should precede the dc operation. Is there any problem, if the dc operation precedes the store operation?

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STATE: TASK_UNINTERRUPTIBLE (PANIC)
by Marc Smith Nov. 11, 2020

Nov. 11, 2020

Hi, I have an issue with the 'bcache' Linux subsystem (block I/O cache). I hit a kernel panic when using this software, and I've reported that upstream on the "linux-bcache" mailing list: https://www.spinics.net/lists/linux-bcache/msg09069.html I'd like to contribute and learn more on how to debug this myself. Here is the output from 'crash' on a dumpfile from this panic: SYSTEM MAP: /home/marc.smith/Downloads/System.map-esos.prod DEBUG KERNEL: /home/marc.smith/Downloads/vmlinux-esos.prod (5.4.69-esos.prod) DUMPFILE: /home/marc.smith/Downloads/dumpfile-1604062993 CPUS: 8 DATE: Fri Oct 30 09:02:56 2020 UPTIME: 2 days, 12:38:15 LOAD AVERAGE: 9.48, 8.89, 7.69 TASKS: 980 NODENAME: node-10cccd-2 RELEASE: 5.4.69-esos.prod VERSION: #1 SMP Thu Oct 22 19:45:11 UTC 2020 MACHINE: x86_64 (2799 Mhz) MEMORY: 24 GB PANIC: "Oops: 0002 [#1] SMP NOPTI" (check log for details) PID: 18272 COMMAND: "kworker/2:13" TASK: ffff88841d9e8000 [THREAD_INFO: ffff88841d9e8000] CPU: 2 STATE: TASK_UNINTERRUPTIBLE (PANIC) crash> bt PID: 18272 TASK: ffff88841d9e8000 CPU: 2 COMMAND: "kworker/2:13" #0 [ffffc90000100938] machine_kexec at ffffffff8103d6b5 #1 [ffffc90000100980] __crash_kexec at ffffffff8110d37b #2 [ffffc90000100a48] crash_kexec at ffffffff8110e07d #3 [ffffc90000100a58] oops_end at ffffffff8101a9de #4 [ffffc90000100a78] no_context at ffffffff81045e99 #5 [ffffc90000100ae0] async_page_fault at ffffffff81e010cf [exception RIP: atomic_try_cmpxchg+2] RIP: ffffffff810d3e3b RSP: ffffc90000100b98 RFLAGS: 00010046 RAX: 0000000000000000 RBX: 0000000000000003 RCX: 0000000000080006 RDX: 0000000000000001 RSI: ffffc90000100ba4 RDI: 0000000000000a6c RBP: 0000000000000010 R8: 0000000000000001 R9: ffffffffa0418d4e R10: ffff88841c8b3000 R11: ffff88841c8b3000 R12: 0000000000000046 R13: 0000000000000000 R14: ffff8885a3a0a000 R15: 0000000000000a6c ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 #6 [ffffc90000100b98] _raw_spin_lock_irqsave at ffffffff81cf7d7d #7 [ffffc90000100bb8] try_to_wake_up at ffffffff810c1624 #8 [ffffc90000100c08] closure_sync_fn at ffffffffa040fb07 [bcache] #9 [ffffc90000100c10] clone_endio at ffffffff81aac48c #10 [ffffc90000100c40] call_bio_endio at ffffffff81a78e20 #11 [ffffc90000100c58] raid_end_bio_io at ffffffff81a78e69 #12 [ffffc90000100c88] raid1_end_write_request at ffffffff81a79ad9 #13 [ffffc90000100cf8] blk_update_request at ffffffff814c3ab1 #14 [ffffc90000100d38] blk_mq_end_request at ffffffff814caaf2 #15 [ffffc90000100d50] blk_mq_complete_request at ffffffff814c91c1 #16 [ffffc90000100d78] nvme_complete_cqes at ffffffffa002fb03 [nvme] #17 [ffffc90000100db8] nvme_irq at ffffffffa002fb7f [nvme] #18 [ffffc90000100de0] __handle_irq_event_percpu at ffffffff810e0d60 #19 [ffffc90000100e20] handle_irq_event_percpu at ffffffff810e0e65 #20 [ffffc90000100e48] handle_irq_event at ffffffff810e0ecb #21 [ffffc90000100e60] handle_edge_irq at ffffffff810e494d #22 [ffffc90000100e78] do_IRQ at ffffffff81e01900 #23 [ffffc90000100eb0] common_interrupt at ffffffff81e00a0a #24 [ffffc90000100f38] __softirqentry_text_start at ffffffff8200006a #25 [ffffc90000100fc8] irq_exit at ffffffff810a3f6a #26 [ffffc90000100fd0] smp_apic_timer_interrupt at ffffffff81e020b2 bt: invalid kernel virtual address: ffffc90000101000 type: "pt_regs" crash> Looking at the call trace, I see this was the last function from 'bcache' in the trace (linux-5.4.69/drivers/md/bcache/closure.c): static void closure_sync_fn(struct closure *cl) { struct closure_syncer *s = cl->s; struct task_struct *p; rcu_read_lock(); p = READ_ONCE(s->task); s->done = 1; wake_up_process(p); rcu_read_unlock(); } And I believe the calls above this in my crash-backtrace output come from this call: wake_up_process() Is the panic perhaps because the task/process is already gone/finished? Not sure where to start looking next. Any help would be greatly appreciated. --Marc

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PCI / PCIe Device Memory - Rationale for Choosing MMIO Over PMIO (and Visa-Versa)
by Jack Winch Nov. 5, 2020

Nov. 5, 2020

Hi all, Over the last couple of months, I've been reading the hardware documentation and Linux device driver source code for a range of different PCI and PCIe devices. Those examined range from multi-function data acquisition cards through to avionics bus interface devices. In doing so, I have referenced numerous resources (including the Third Edition of LDD - what a great book - and the documentation available for the Linux PCI Bus Subsystem on kernel.org) One thing I'm still a little unclear on is why vendors might opt to map PCI / PCIe device memory into the system memory map as either Memory-Mapped I/O (MMIO) or Port-Mapped I/O (PMIO). That is, for what reasons would a device manufacturer choose to make use of one address space over the other for regions of a PCI / PCIe device's memory? Some of the general reasons are alluded to by the aforementioned resources (e.g., more instruction cycles are required to access data via PMIO, MMIO can be marked as prefetchable and handled as such, etc). Would anyone who's been engaged in the development of a PCI / PCIe device talk about their experience and what factors led to one address space being chosen over the other (for specific regions of a specific device)? Specific examples would really help me (and probably others) understand what factors are involved in this decision and how a suitable choice is made. Reading the driver source code, for specific devices, has been great for developing an initial understanding of the different approaches taken by device manufacturers, but source code and hardware documentation rarely provide any information on the rationale for a chosen implementation. Any specific technical accounts on this matter, etc, would be much appreciated. Jack

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initialization of global variables in u-boot
by Tomek The Messenger Nov. 4, 2020

Nov. 4, 2020

Hi As there is none u-boot mailing list anymore I will ask question here. Maybe someone will know answer. I have two watchdogs in hardware. One is synopsys designware one (so standard u-boot global functions hw_watchdog_init and hw_watchdog_reset are implemented by open source synopsys designware driver. And I have second watchdog for which I implement my own driver and it bases on device tree model. Let's see at below code: include/watchdog.h (I added second config and modify macro WATCHDOG_RESET) [code] extern void hw_watchdog_reset(void); #if defined(CONFIG_DM_HW_WATCHDOG) extern void dm_hw_watchdog_reset(void); #define WATCHDOG_RESET() {hw_watchdog_reset(); dm_hw_watchdog_reset();} #else #define WATCHDOG_RESET hw_watchdog_reset #endif [/code] implementation of dm_hw_watchdog_reset function: [code] #ifndef CONFIG_SPL_BUILD struct udevice* wdt = NULL; void dm_hw_watchdog_reset(void) { int ret; if (wdt) { printf("dm_hw_watchdog_reset\n"); wdt_reset(wdt); } else { ret = 2+8; /*ret = uclass_get_device_by_driver(UCLASS_WDT, DM_GET_DRIVER(wdt_bmu), &wdt); if (ret) printf("Lack of watchdog device\n"); else wdt_start(wdt, 60000, 0);*/ } } #else void dm_hw_watchdog_reset(void) { } #endif [/code] What is weird when Uboot is started it prints tens of times: " dm_hw_watchdog_reset" and then hangs on. I have to power on/off the board and recovery it with the aid of jtag. I don't understand why 'wdt' variable isn't NULL and code under if (wdt) is executed. Seems like something uboot specific.

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