From: Arkady <arkady.miasnikov@gmail.com>
To: Kun <mingkunone@qq.com>
Cc: Serhei Makarov <smakarov@redhat.com>,
systemtap <systemtap@sourceware.org>
Subject: Re: Fwd: systemtap global var lead to high cpu
Date: Fri, 24 Jul 2020 06:49:44 +0300 [thread overview]
Message-ID: <CANA-60r1N7Fo14LY9S5g_UWnGrLUo+mAiX+K7snc2+CmCz7SwA@mail.gmail.com> (raw)
In-Reply-To: <tencent_72B9E9310FED38F95B6463947837896AD107@qq.com>
Hi Kun,
I avoid locks by using lockless data structures. For example, I have
my own hashtables instead of associative arrays.
You can check this code for inspiration
https://github.com/larytet/lockfree_hashtable
If the performance is paramount for your task you can switch to 100%
handwritten C code.
Arkady,
On Fri, Jul 24, 2020 at 5:01 AM Kun via Systemtap
<systemtap@sourceware.org> wrote:
>
> My global var saved is string type, not number, so I can not use aggregate.
> FChE will fixed this bug,
> https://sourceware.org/bugzilla/show_bug.cgi?id=26296
> Hoping to fixed soon.
>
>
>
>
> ------------------ Original ------------------
> From: Serhei Makarov <smakarov@redhat.com>
> Date: Thu,Jul 23,2020 10:22 PM
> To: systemtap <systemtap@sourceware.org>, mingkunone <mingkunone@qq.com>
> Subject: Re: Fwd: systemtap global var lead to high cpu
>
>
>
> Forwarding your question to systemtap@sourceware.org in case other people have suggestions.
>
>
>
> In general, the locks protect concurrent modifications from interfering with each other when different processes trigger the same probe.
>
>
> Depending on what you want to do with the iphdr value, you may be able to reduce contention by using statistical aggregates
> (which do not require locking). For example, aaa[iphdr] <<< some_statistic; in a later probe iterate through aaa. A lot of the SystemTap example scripts use this type of structure, for example: https://sourceware.org/systemtap/examples/network/netfilter_summary.stp
>
>
> Otherwise, every tcp_ack() for every packet on your system will try to grab the same lock. The resulting CPU load is unsurprising to me.
>
>
> Hope this information is helpful; if not, someone else may have a better suggestion.
>
>
> All the best,
> Serhei
>
>
> ---------- Forwarded message ---------
> From: Kun <mingkunone@qq.com>
> Date: Wed, Jul 22, 2020 at 11:24 PM
> Subject: systemtap global var lead to high cpu
> To: smakarov <smakarov@redhat.com>
>
>
>
> Hi,
> I have a problem of system tap which
> Using global var.
> A simple demo as following,
> Global aaa
> Probe kernel.function(“tcp_ack”){
> Iphdr = __get_skb_iphdr($skb)
> If(iphdr == 0){
> aaa=iphdr
> }
>
>
> Then our env have a 10Gbps flow, and our cpu is nearly 100%.
>
>
> Analysising c code, I find this is because of a lock as following:
> Static void probe_6330()
> {
> If(sta_lock_probe(lock, ARRAY_SIZE(locks))
> Return;
> If(l->iphdr == 0){
> Global(s_global_aaa)=l->l_iphdr;
> }
>
>
> My question is that aaa should be protected in “if”,
> Why is the lock directly at the function entry?
next prev parent reply other threads:[~2020-07-24 3:49 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-24 2:00 Kun
2020-07-24 3:49 ` Arkady [this message]
2020-07-25 2:45 ` Kun
2020-07-25 5:25 ` Arkady
2020-08-18 19:11 ` Frank Ch. Eigler
[not found] <tencent_FB0905D58DA3FA7F0E728C535B447E0D1905@qq.com>
2020-07-23 14:22 ` Serhei Makarov
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