Re: more of a linux question

Thank you Mladen, all,

First I made a mistake, is RHEL8 (not RHEL7) vs RHEL6. I thought I had a CPU problem due to VMware layer, but it seems like my script is running in equal amounts of time in both rhel6/8 if executed under KSH and not BASH.

Now these are application servers so as of now I`m trying to understand if behavior I see for bash will also impact weblogic/oracle bi. But indeed seems like RHEL8 is bringing some optimizations which can prove significant (at least for my test) compared with RHEL6

În sâm., 14 oct. 2023 la 02:54, Mladen Gogala <gogala.mladen_at_gmail.com> a scris:

> On 10/12/23 06:35, Laurentiu Oprea wrote:
>
> Dear all,
>
> I`m having a linux question, I know it is not the right place but I know
> for sure we have some linux gurus around.
>
> I`m trying to figure out why a simple bash loop like (pseudocode) : while
> i < n do i=i+1 end for similar hardware is running in 30 seconds on RHEL7
> servers but in 75 on RHEL6.
>
> I did a perf tracing on each process and I can observe that sigprocmask
> function call is accountable for around 20% of time in RHEL6 while in RHEL7
> is not even present.
>
> THere are couple of other functions not present in RHEL7 but only in RHEL6
> like: strcpy_ssse3 (3% of time) , and some functions which runs 3 times
> faster on RHEL7 like mbrtowc 9.5% in RHEL6 vs 3.5% in RHEL7
>
> DO you guys think it is a matter of just a newer / faster kernel? maybe
> other libraries involved like glibc?
>
> Appreciate your feedback.
>
> Well, sigprocmask is a function which examines which signals are blocked
> from delivery, It should work on the process header and complete relatively
> quickly:
>
> NAME
> sigprocmask, rt_sigprocmask - examine and change blocked signals
>
> LIBRARY
> Standard C library (libc, -lc)
>
> SYNOPSIS
> #include <signal.h>
>
> /* Prototype for the glibc wrapper function */
> int sigprocmask(int how, const sigset_t *_Nullable restrict set,
> sigset_t *_Nullable restrict oldset);
>
> #include <signal.h> /* Definition of SIG_* constants */
> #include <sys/syscall.h> /* Definition of SYS_* constants */
> #include <unistd.h>
>
> /* Prototype for the underlying system call */
> int syscall(SYS_rt_sigprocmask, int how,
> const kernel_sigset_t *_Nullable set,
> kernel_sigset_t *_Nullable oldset,
> size_t sigsetsize);
>
> Other than that, I too have noticed increased speed on RHEL8, as opposed
> to RHEL7. I believe that we are seeing improved algorithms in newer
> kernels, Some of it is advertised, like here:
>
>
> https://www.zdnet.com/article/linux-6-0-arrives-with-performance-improvements-and-more-rust-coming/
>
> Also, newer kernels have drivers for NVME devices, which were not
> available in RHEL6. Furthermore, one of the standard performance tuning
> advices is "update your kernel":
>
>
> https://kernelgrok.com/optimizing-the-linux-kernel-tips-to-improve-performance/
>
> In other words, I kind of expect newer versions of Linux to be better than
> the old versions of Linux.
>
> --
> Mladen Gogala
> Database Consultant
> Tel: (347) 321-1217https://dbwhisperer.wordpress.com
>
>

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