need help for avoiding system calls while using URCU (Userspace RCU)

need help for avoiding system calls while using URCU (Userspace RCU)

[方锴 via lttng-dev]

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Dear 

I have referenced your project, URCU (Userspace RCU), on GitHub, which is based on the QSBR model. However, I noticed that when using it in user mode, it makes system calls to enter the kernel. Could you please provide guidance on how to address this issue? I aim to achieve a pure user-mode implementation. Specifically, I would appreciate any insights or suggestions on avoiding system calls while still maintaining the functionality of the QSBR model in user space. Thank you very much for your time and assistance.



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Re: need help for avoiding system calls while using URCU (Userspace RCU)

[Kienan Stewart via lttng-dev]

Hi 方锴,

On 3/4/25 3:09 AM, 方锴 via lttng-dev wrote:

> I have referenced your project, URCU (Userspace RCU), on GitHub, which is based on the QSBR model. However, I 
noticed that when using it in user mode, it makes system calls to enter 
the kernel. Could you please provide guidance on how to address this issue?

Are there specific parts of the API that you need to be user-space only?

 > I aim to achieve a pure user-mode implementation. Specifically, I 
would appreciate any insights or suggestions on avoiding system calls 
while still maintaining the functionality of the QSBR model in user 
space. Thank you very much for your time and assistance.

Currently the locking is done using futexs, which are system calls. 
Those could potentially be replaced with a poll/retry system either in a 
different flavour of URCU or at build-time.

thanks,
kienan

Re: need help for avoiding system calls while using URCU (Userspace RCU)

[Mathieu Desnoyers via lttng-dev]

On 2025-03-06 11:17, Kienan Stewart via lttng-dev wrote:
> Hi 方锴,
> 
> On 3/4/25 3:09 AM, 方锴 via lttng-dev wrote:
> 
>> I have referenced your project, URCU (Userspace RCU), on GitHub, which 
>> is based on the QSBR model. However, I 
> noticed that when using it in user mode, it makes system calls to enter 
> the kernel. Could you please provide guidance on how to address this issue?
> 
> Are there specific parts of the API that you need to be user-space only?
> 
>  > I aim to achieve a pure user-mode implementation. Specifically, I 
> would appreciate any insights or suggestions on avoiding system calls 
> while still maintaining the functionality of the QSBR model in user 
> space. Thank you very much for your time and assistance.
> 
> Currently the locking is done using futexs, which are system calls. 

Clarification: the wait/wakeup between read-side and synchronize is done
using the futex system call. There is no locking on the read-side
per-se.

Thanks,

Mathieu

> Those could potentially be replaced with a poll/retry system either in a 
> different flavour of URCU or at build-time.
> 
> thanks,
> kienan


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

Re:Re: need help for avoiding system calls while using URCU (Userspace RCU)

[方锴 via lttng-dev]

dear kienan<br/>Thank you for your guidance, I've found DKDP's URCU successfully avoids system calls. Grateful for your support!<br/>Best regards,<br/>fangkai
At 2025-03-07 00:17:34, "Kienan Stewart" <kstewart@efficios.com> wrote:
>Hi 方锴,
>
>On 3/4/25 3:09 AM, 方锴 via lttng-dev wrote:
>
>> I have referenced your project, URCU (Userspace RCU), on GitHub, which is based on the QSBR model. However, I 
>noticed that when using it in user mode, it makes system calls to enter 
>the kernel. Could you please provide guidance on how to address this issue?
>
>Are there specific parts of the API that you need to be user-space only?
>
> > I aim to achieve a pure user-mode implementation. Specifically, I 
>would appreciate any insights or suggestions on avoiding system calls 
>while still maintaining the functionality of the QSBR model in user 
>space. Thank you very much for your time and assistance.
>
>Currently the locking is done using futexs, which are system calls. 
>Those could potentially be replaced with a poll/retry system either in a 
>different flavour of URCU or at build-time.
>
>thanks,
>kienan

Re:Re: need help for avoiding system calls while using URCU (Userspace RCU)

[方锴 via lttng-dev]

dear Mathieu<br/>  Thank you for your guidance, I've found DKDP's URCU successfully avoids system calls. Grateful for your support!<br/>Best regards,<br/>fangkai
At 2025-03-07 00:58:21, "Mathieu Desnoyers" <mathieu.desnoyers@efficios.com> wrote:
>On 2025-03-06 11:17, Kienan Stewart via lttng-dev wrote:
>> Hi 方锴,
>> 
>> On 3/4/25 3:09 AM, 方锴 via lttng-dev wrote:
>> 
>>> I have referenced your project, URCU (Userspace RCU), on GitHub, which 
>>> is based on the QSBR model. However, I 
>> noticed that when using it in user mode, it makes system calls to enter 
>> the kernel. Could you please provide guidance on how to address this issue?
>> 
>> Are there specific parts of the API that you need to be user-space only?
>> 
>>  > I aim to achieve a pure user-mode implementation. Specifically, I 
>> would appreciate any insights or suggestions on avoiding system calls 
>> while still maintaining the functionality of the QSBR model in user 
>> space. Thank you very much for your time and assistance.
>> 
>> Currently the locking is done using futexs, which are system calls. 
>
>Clarification: the wait/wakeup between read-side and synchronize is done
>using the futex system call. There is no locking on the read-side
>per-se.
>
>Thanks,
>
>Mathieu
>
>> Those could potentially be replaced with a poll/retry system either in a 
>> different flavour of URCU or at build-time.
>> 
>> thanks,
>> kienan
>
>
>-- 
>Mathieu Desnoyers
>EfficiOS Inc.
>https://www.efficios.com