Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[Yafang Shao]

On Wed, Apr 18, 2018 at 7:44 AM, Alexei Starovoitov
 wrote:
> On Mon, Apr 16, 2018 at 08:43:31AM -0700, Eric Dumazet wrote:
>>
>>
>> On 04/16/2018 08:33 AM, Yafang Shao wrote:
>> > tcp_rcv_space_adjust is called every time data is copied to user space,
>> > introducing a tcp tracepoint for which could show us when the packet is
>> > copied to user.
>> > This could help us figure out whether there's latency in user process.
>> >
>> > When a tcp packet arrives, tcp_rcv_established() will be called and with
>> > the existed tracepoint tcp_probe we could get the time when this packet
>> > arrives.
>> > Then this packet will be copied to user, and tcp_rcv_space_adjust will
>> > be called and with this new introduced tracepoint we could get the time
>> > when this packet is copied to user.
>> >
>> > arrives time : user process time=> latency caused by user
>> > tcp_probe  tcp_rcv_space_adjust
>> >
>> > Hence in the prink message, sk is printed as a key to connect these two
>> > tracepoints.
>> >
>>
>> socket pointer is not a key.
>>
>> TCP sockets can be reused pretty fast after free.
>>
>> I suggest you go for cookie instead, this is an unique 64bit identifier.
>> ( sock_gen_cookie() for details )
>
> I think would be even better if the stack would do this sock_gen_cookie()
> on its own in some way that user cannnot infere the order.
> In many cases we wanted to use socket cookie, but since it's not inited
> by default it's kinda useless.
> Turning this tracepoint on just to get cookie would be an ugly workaround.
>

Could we init it in sk_alloc() ?
Then in other code paths, for example sock_getsockopt or tracepoints,
we only read the value through a new inline function named
sock_read_cookie().


Thanks
Yafang

Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[Yafang Shao]

On Wed, Apr 18, 2018 at 7:44 AM, Alexei Starovoitov
 wrote:
> On Mon, Apr 16, 2018 at 08:43:31AM -0700, Eric Dumazet wrote:
>>
>>
>> On 04/16/2018 08:33 AM, Yafang Shao wrote:
>> > tcp_rcv_space_adjust is called every time data is copied to user space,
>> > introducing a tcp tracepoint for which could show us when the packet is
>> > copied to user.
>> > This could help us figure out whether there's latency in user process.
>> >
>> > When a tcp packet arrives, tcp_rcv_established() will be called and with
>> > the existed tracepoint tcp_probe we could get the time when this packet
>> > arrives.
>> > Then this packet will be copied to user, and tcp_rcv_space_adjust will
>> > be called and with this new introduced tracepoint we could get the time
>> > when this packet is copied to user.
>> >
>> > arrives time : user process time=> latency caused by user
>> > tcp_probe  tcp_rcv_space_adjust
>> >
>> > Hence in the prink message, sk is printed as a key to connect these two
>> > tracepoints.
>> >
>>
>> socket pointer is not a key.
>>
>> TCP sockets can be reused pretty fast after free.
>>
>> I suggest you go for cookie instead, this is an unique 64bit identifier.
>> ( sock_gen_cookie() for details )
>
> I think would be even better if the stack would do this sock_gen_cookie()
> on its own in some way that user cannnot infere the order.
> In many cases we wanted to use socket cookie, but since it's not inited
> by default it's kinda useless.
> Turning this tracepoint on just to get cookie would be an ugly workaround.
>

Could we init it in sk_alloc() ?
Then in other code paths, for example sock_getsockopt or tracepoints,
we only read the value through a new inline function named
sock_read_cookie().


Thanks
Yafang

Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[Alexei Starovoitov]

On Mon, Apr 16, 2018 at 08:43:31AM -0700, Eric Dumazet wrote:
> 
> 
> On 04/16/2018 08:33 AM, Yafang Shao wrote:
> > tcp_rcv_space_adjust is called every time data is copied to user space,
> > introducing a tcp tracepoint for which could show us when the packet is
> > copied to user.
> > This could help us figure out whether there's latency in user process.
> > 
> > When a tcp packet arrives, tcp_rcv_established() will be called and with
> > the existed tracepoint tcp_probe we could get the time when this packet
> > arrives.
> > Then this packet will be copied to user, and tcp_rcv_space_adjust will
> > be called and with this new introduced tracepoint we could get the time
> > when this packet is copied to user.
> > 
> > arrives time : user process time=> latency caused by user
> > tcp_probe  tcp_rcv_space_adjust
> > 
> > Hence in the prink message, sk is printed as a key to connect these two
> > tracepoints.
> > 
> 
> socket pointer is not a key.
> 
> TCP sockets can be reused pretty fast after free.
> 
> I suggest you go for cookie instead, this is an unique 64bit identifier.
> ( sock_gen_cookie() for details )

I think would be even better if the stack would do this sock_gen_cookie()
on its own in some way that user cannnot infere the order.
In many cases we wanted to use socket cookie, but since it's not inited
by default it's kinda useless.
Turning this tracepoint on just to get cookie would be an ugly workaround.

Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[Alexei Starovoitov]

On Mon, Apr 16, 2018 at 08:43:31AM -0700, Eric Dumazet wrote:
> 
> 
> On 04/16/2018 08:33 AM, Yafang Shao wrote:
> > tcp_rcv_space_adjust is called every time data is copied to user space,
> > introducing a tcp tracepoint for which could show us when the packet is
> > copied to user.
> > This could help us figure out whether there's latency in user process.
> > 
> > When a tcp packet arrives, tcp_rcv_established() will be called and with
> > the existed tracepoint tcp_probe we could get the time when this packet
> > arrives.
> > Then this packet will be copied to user, and tcp_rcv_space_adjust will
> > be called and with this new introduced tracepoint we could get the time
> > when this packet is copied to user.
> > 
> > arrives time : user process time=> latency caused by user
> > tcp_probe  tcp_rcv_space_adjust
> > 
> > Hence in the prink message, sk is printed as a key to connect these two
> > tracepoints.
> > 
> 
> socket pointer is not a key.
> 
> TCP sockets can be reused pretty fast after free.
> 
> I suggest you go for cookie instead, this is an unique 64bit identifier.
> ( sock_gen_cookie() for details )

I think would be even better if the stack would do this sock_gen_cookie()
on its own in some way that user cannnot infere the order.
In many cases we wanted to use socket cookie, but since it's not inited
by default it's kinda useless.
Turning this tracepoint on just to get cookie would be an ugly workaround.

Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[Yafang Shao]

On Mon, Apr 16, 2018 at 11:43 PM, Eric Dumazet  wrote:
>
>
> On 04/16/2018 08:33 AM, Yafang Shao wrote:
>> tcp_rcv_space_adjust is called every time data is copied to user space,
>> introducing a tcp tracepoint for which could show us when the packet is
>> copied to user.
>> This could help us figure out whether there's latency in user process.
>>
>> When a tcp packet arrives, tcp_rcv_established() will be called and with
>> the existed tracepoint tcp_probe we could get the time when this packet
>> arrives.
>> Then this packet will be copied to user, and tcp_rcv_space_adjust will
>> be called and with this new introduced tracepoint we could get the time
>> when this packet is copied to user.
>>
>>   arrives time : user process time=> latency caused by user
>>   tcp_probe  tcp_rcv_space_adjust
>>
>> Hence in the prink message, sk is printed as a key to connect these two
>> tracepoints.
>>
>
> socket pointer is not a key.
>
> TCP sockets can be reused pretty fast after free.
>
> I suggest you go for cookie instead, this is an unique 64bit identifier.
> ( sock_gen_cookie() for details )
>
>

Thanks for your explanation.
Will have a try.

Thanks
Yafang

Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[Yafang Shao]

On Mon, Apr 16, 2018 at 11:43 PM, Eric Dumazet  wrote:
>
>
> On 04/16/2018 08:33 AM, Yafang Shao wrote:
>> tcp_rcv_space_adjust is called every time data is copied to user space,
>> introducing a tcp tracepoint for which could show us when the packet is
>> copied to user.
>> This could help us figure out whether there's latency in user process.
>>
>> When a tcp packet arrives, tcp_rcv_established() will be called and with
>> the existed tracepoint tcp_probe we could get the time when this packet
>> arrives.
>> Then this packet will be copied to user, and tcp_rcv_space_adjust will
>> be called and with this new introduced tracepoint we could get the time
>> when this packet is copied to user.
>>
>>   arrives time : user process time=> latency caused by user
>>   tcp_probe  tcp_rcv_space_adjust
>>
>> Hence in the prink message, sk is printed as a key to connect these two
>> tracepoints.
>>
>
> socket pointer is not a key.
>
> TCP sockets can be reused pretty fast after free.
>
> I suggest you go for cookie instead, this is an unique 64bit identifier.
> ( sock_gen_cookie() for details )
>
>

Thanks for your explanation.
Will have a try.

Thanks
Yafang

Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[Eric Dumazet]

On 04/16/2018 08:33 AM, Yafang Shao wrote:
> tcp_rcv_space_adjust is called every time data is copied to user space,
> introducing a tcp tracepoint for which could show us when the packet is
> copied to user.
> This could help us figure out whether there's latency in user process.
> 
> When a tcp packet arrives, tcp_rcv_established() will be called and with
> the existed tracepoint tcp_probe we could get the time when this packet
> arrives.
> Then this packet will be copied to user, and tcp_rcv_space_adjust will
> be called and with this new introduced tracepoint we could get the time
> when this packet is copied to user.
> 
>   arrives time : user process time=> latency caused by user
>   tcp_probe  tcp_rcv_space_adjust
> 
> Hence in the prink message, sk is printed as a key to connect these two
> tracepoints.
> 

socket pointer is not a key.

TCP sockets can be reused pretty fast after free.

I suggest you go for cookie instead, this is an unique 64bit identifier.
( sock_gen_cookie() for details )

Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[Eric Dumazet]

On 04/16/2018 08:33 AM, Yafang Shao wrote:
> tcp_rcv_space_adjust is called every time data is copied to user space,
> introducing a tcp tracepoint for which could show us when the packet is
> copied to user.
> This could help us figure out whether there's latency in user process.
> 
> When a tcp packet arrives, tcp_rcv_established() will be called and with
> the existed tracepoint tcp_probe we could get the time when this packet
> arrives.
> Then this packet will be copied to user, and tcp_rcv_space_adjust will
> be called and with this new introduced tracepoint we could get the time
> when this packet is copied to user.
> 
>   arrives time : user process time=> latency caused by user
>   tcp_probe  tcp_rcv_space_adjust
> 
> Hence in the prink message, sk is printed as a key to connect these two
> tracepoints.
> 

socket pointer is not a key.

TCP sockets can be reused pretty fast after free.

I suggest you go for cookie instead, this is an unique 64bit identifier.
( sock_gen_cookie() for details )

Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[David Miller]

The net-next tree is closed, please resubmit this when the merge window
ends and the net-next tree opens back up.

Thank you.

Re: [PATCH net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[David Miller]

The net-next tree is closed, please resubmit this when the merge window
ends and the net-next tree opens back up.

Thank you.