[PATCH] tcp: remove obsolete paramter sysctl_tcp_low_latency

[PATCH] tcp: remove obsolete paramter sysctl_tcp_low_latency

[lyl]

Remove tcp_low_latency, since it is not functional After commit
e7942d0633c4 (tcp: remove prequeue support)

Signed-off-by: lyl <liyonglong@chinatelecom.cn>
---
 net/ipv4/sysctl_net_ipv4.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 3e5f4f2..d03e4c0 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -51,9 +51,6 @@
 static u32 u32_max_div_HZ = UINT_MAX / HZ;
 static int one_day_secs = 24 * 3600;
 
-/* obsolete */
-static int sysctl_tcp_low_latency __read_mostly;
-
 /* Update system visible IP port range */
 static void set_local_port_range(struct net *net, int range[2])
 {
@@ -501,13 +498,6 @@ static int proc_fib_multipath_hash_policy(struct ctl_table *table, int write,
 		.mode		= 0644,
 		.proc_handler	= proc_doulongvec_minmax,
 	},
-	{
-		.procname	= "tcp_low_latency",
-		.data		= &sysctl_tcp_low_latency,
-		.maxlen		= sizeof(int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec
-	},
 #ifdef CONFIG_NETLABEL
 	{
 		.procname	= "cipso_cache_enable",
-- 
1.8.3.1

Re: [PATCH] tcp: remove obsolete paramter sysctl_tcp_low_latency

[Jakub Kicinski]

On Fri, 18 Dec 2020 14:11:16 +0800 lyl wrote:
> Remove tcp_low_latency, since it is not functional After commit
> e7942d0633c4 (tcp: remove prequeue support)
> 
> Signed-off-by: lyl <liyonglong@chinatelecom.cn>

I don't think we can remove sysctls, even if they no longer control 
the behavior of the kernel. The existence of the file itself is uAPI.

Re: [PATCH] tcp: remove obsolete paramter sysctl_tcp_low_latency

[lll]

在 2020/12/19 8:46, Jakub Kicinski 写道:
> On Fri, 18 Dec 2020 14:11:16 +0800 lyl wrote:
>> Remove tcp_low_latency, since it is not functional After commit
>> e7942d0633c4 (tcp: remove prequeue support)
>>
>> Signed-off-by: lyl <liyonglong@chinatelecom.cn>
> 
> I don't think we can remove sysctls, even if they no longer control 
> the behavior of the kernel. The existence of the file itself is uAPI.
> 
Got it. But a question: why tcp_tw_recycle can be removed totally?  it is also part of uAPI

Re: [PATCH] tcp: remove obsolete paramter sysctl_tcp_low_latency

[Jakub Kicinski]

On Thu, 7 Jan 2021 11:08:16 +0800 lll wrote:
> 在 2020/12/19 8:46, Jakub Kicinski 写道:
> > On Fri, 18 Dec 2020 14:11:16 +0800 lyl wrote:  
> >> Remove tcp_low_latency, since it is not functional After commit
> >> e7942d0633c4 (tcp: remove prequeue support)
> >>
> >> Signed-off-by: lyl <liyonglong@chinatelecom.cn>  
> > 
> > I don't think we can remove sysctls, even if they no longer control 
> > the behavior of the kernel. The existence of the file itself is uAPI.
>
> Got it. But a question: why tcp_tw_recycle can be removed totally?
> it is also part of uAPI

Good question, perhaps with tcp_tw_recycle we wanted to make sure users
who depended on it notice removal, since the feature was broken by
design? 

tcp_low_latency is an optimization, not functionality which users may
depend on.

But I may be wrong so CCing authors.

Re: [PATCH] tcp: remove obsolete paramter sysctl_tcp_low_latency

[Florian Westphal]

Jakub Kicinski <kuba@kernel.org> wrote:
> > Got it. But a question: why tcp_tw_recycle can be removed totally?
> > it is also part of uAPI
> 
> Good question, perhaps with tcp_tw_recycle we wanted to make sure users
> who depended on it notice removal, since the feature was broken by
> design? 
> 
> tcp_low_latency is an optimization, not functionality which users may
> depend on.
> 
> But I may be wrong so CCing authors.

I guess it was just a case of 'noone noticed'.
I'm not sure if anyone would notice dropping lowlatency sysctl, was just
a case of 'overly careful'.  Personally I'd rather have them gone so
'sysctl tcp.bla' shows if the feature exists/does something.