[iproute2-next] Improve batch times by caching link lookups

Message ID 20190107204130.32144-1-dsahern@kernel.org
State Changes Requested
Delegated to: David Ahern
Headers show
Series
  • [iproute2-next] Improve batch times by caching link lookups
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Commit Message

David Ahern Jan. 7, 2019, 8:41 p.m.
From: David Ahern <dsahern@gmail.com>

ip route uses ll_name_to_index to convert the user given device name to an
index. At the moment ll_name_to_index uses if_nametoindex which is ioctl
based and does not cache the result. When using a batch file this means
the same device lookups can be done repeatedly adding unnecessary overhead
(socket + ioctl call for each device lookup).

Add a new function, ll_link_get, to send a netlink based RTM_GETLINK. If
successful, cache the result in idx_head and name_head so future lookups
can re-use the entry.

With this change the time to install routes via a batch file is reduced
from 30.7 seconds to 17.6 seconds (720,022 routes with 2 ecmp nexthops
where the nexthop device is given).

Signed-off-by: David Ahern <dsahern@gmail.com>
---
 lib/ll_map.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

Comments

Eric Dumazet Jan. 7, 2019, 8:57 p.m. | #1
On 01/07/2019 12:41 PM, David Ahern wrote:
> From: David Ahern <dsahern@gmail.com>
> 
> ip route uses ll_name_to_index to convert the user given device name to an
> index. At the moment ll_name_to_index uses if_nametoindex which is ioctl
> based and does not cache the result. When using a batch file this means
> the same device lookups can be done repeatedly adding unnecessary overhead
> (socket + ioctl call for each device lookup).
> 
> Add a new function, ll_link_get, to send a netlink based RTM_GETLINK. If
> successful, cache the result in idx_head and name_head so future lookups
> can re-use the entry.
> 
> With this change the time to install routes via a batch file is reduced
> from 30.7 seconds to 17.6 seconds (720,022 routes with 2 ecmp nexthops
> where the nexthop device is given).
> 

What time increase if we have 10,000 devices, and install one route ?

Caching 10,000 devices would be quite a waste.
David Ahern Jan. 7, 2019, 8:58 p.m. | #2
On 1/7/19 1:57 PM, Eric Dumazet wrote:
> 
> 
> On 01/07/2019 12:41 PM, David Ahern wrote:
>> From: David Ahern <dsahern@gmail.com>
>>
>> ip route uses ll_name_to_index to convert the user given device name to an
>> index. At the moment ll_name_to_index uses if_nametoindex which is ioctl
>> based and does not cache the result. When using a batch file this means
>> the same device lookups can be done repeatedly adding unnecessary overhead
>> (socket + ioctl call for each device lookup).
>>
>> Add a new function, ll_link_get, to send a netlink based RTM_GETLINK. If
>> successful, cache the result in idx_head and name_head so future lookups
>> can re-use the entry.
>>
>> With this change the time to install routes via a batch file is reduced
>> from 30.7 seconds to 17.6 seconds (720,022 routes with 2 ecmp nexthops
>> where the nexthop device is given).
>>
> 
> What time increase if we have 10,000 devices, and install one route ?
> 
> Caching 10,000 devices would be quite a waste.
> 

It only lookups up the device if ll_name_to_index is invoked for the
device.

This is NOT a link dump and cache; it only adds lookups to the cache.
Eric Dumazet Jan. 7, 2019, 9:06 p.m. | #3
On 01/07/2019 12:58 PM, David Ahern wrote:
> On 1/7/19 1:57 PM, Eric Dumazet wrote:
>>
>>
>> On 01/07/2019 12:41 PM, David Ahern wrote:
>>> From: David Ahern <dsahern@gmail.com>
>>>
>>> ip route uses ll_name_to_index to convert the user given device name to an
>>> index. At the moment ll_name_to_index uses if_nametoindex which is ioctl
>>> based and does not cache the result. When using a batch file this means
>>> the same device lookups can be done repeatedly adding unnecessary overhead
>>> (socket + ioctl call for each device lookup).
>>>
>>> Add a new function, ll_link_get, to send a netlink based RTM_GETLINK. If
>>> successful, cache the result in idx_head and name_head so future lookups
>>> can re-use the entry.
>>>
>>> With this change the time to install routes via a batch file is reduced
>>> from 30.7 seconds to 17.6 seconds (720,022 routes with 2 ecmp nexthops
>>> where the nexthop device is given).
>>>
>>
>> What time increase if we have 10,000 devices, and install one route ?
>>
>> Caching 10,000 devices would be quite a waste.
>>
> 
> It only lookups up the device if ll_name_to_index is invoked for the
> device.
> 
> This is NOT a link dump and cache; it only adds lookups to the cache.
> 

I see, maybe split this in two patches to avoid the confusion.

Why is the RTNETLINK approach better than ioctl() ?

If this is the case, maybe if_nametoindex() should be fixed, instead of carrying this locally in iproute2.
David Ahern Jan. 7, 2019, 9:16 p.m. | #4
On 1/7/19 2:06 PM, Eric Dumazet wrote:
> 
> 
> On 01/07/2019 12:58 PM, David Ahern wrote:
>> On 1/7/19 1:57 PM, Eric Dumazet wrote:
>>>
>>>
>>> On 01/07/2019 12:41 PM, David Ahern wrote:
>>>> From: David Ahern <dsahern@gmail.com>
>>>>
>>>> ip route uses ll_name_to_index to convert the user given device name to an
>>>> index. At the moment ll_name_to_index uses if_nametoindex which is ioctl
>>>> based and does not cache the result. When using a batch file this means
>>>> the same device lookups can be done repeatedly adding unnecessary overhead
>>>> (socket + ioctl call for each device lookup).
>>>>
>>>> Add a new function, ll_link_get, to send a netlink based RTM_GETLINK. If
>>>> successful, cache the result in idx_head and name_head so future lookups
>>>> can re-use the entry.
>>>>
>>>> With this change the time to install routes via a batch file is reduced
>>>> from 30.7 seconds to 17.6 seconds (720,022 routes with 2 ecmp nexthops
>>>> where the nexthop device is given).
>>>>
>>>
>>> What time increase if we have 10,000 devices, and install one route ?
>>>
>>> Caching 10,000 devices would be quite a waste.
>>>
>>
>> It only lookups up the device if ll_name_to_index is invoked for the
>> device.
>>
>> This is NOT a link dump and cache; it only adds lookups to the cache.
>>
> 
> I see, maybe split this in two patches to avoid the confusion.
> 
> Why is the RTNETLINK approach better than ioctl() ?

I could very well cache the if_nametoindex result but that is only name
<--> idx. To avoid making assumptions on how the ll_map code is used in
the future, RTM_GETLINK is used to leverage ll_remember_index and have
the cache entries always be consistently filled.

> 
> If this is the case, maybe if_nametoindex() should be fixed, instead of carrying this locally in iproute2.
> 

if_nametoindex has to do socket() - ioctl() - close() for every device
lookup. It's not a bug and caching the socket descriptor makes
assumptions that libc should not be making.
Stephen Hemminger Jan. 7, 2019, 9:31 p.m. | #5
On Mon,  7 Jan 2019 12:41:30 -0800
David Ahern <dsahern@kernel.org> wrote:

> From: David Ahern <dsahern@gmail.com>
> 
> ip route uses ll_name_to_index to convert the user given device name to an
> index. At the moment ll_name_to_index uses if_nametoindex which is ioctl
> based and does not cache the result. When using a batch file this means
> the same device lookups can be done repeatedly adding unnecessary overhead
> (socket + ioctl call for each device lookup).
> 
> Add a new function, ll_link_get, to send a netlink based RTM_GETLINK. If
> successful, cache the result in idx_head and name_head so future lookups
> can re-use the entry.
> 
> With this change the time to install routes via a batch file is reduced
> from 30.7 seconds to 17.6 seconds (720,022 routes with 2 ecmp nexthops
> where the nexthop device is given).
> 
> Signed-off-by: David Ahern <dsahern@gmail.com>

What if a ip command in the batch does a rename?
David Ahern Jan. 7, 2019, 9:52 p.m. | #6
On 1/7/19 2:31 PM, Stephen Hemminger wrote:
> 
> What if a ip command in the batch does a rename?
> 

Simplest action (meaning least overhead for non-batch) is to drop any
entry from the cache. If a later command needs it, the cache entry can
be re-created.

Patch

diff --git a/lib/ll_map.c b/lib/ll_map.c
index 1ab8ef0758ac..4fbd9fa70dd7 100644
--- a/lib/ll_map.c
+++ b/lib/ll_map.c
@@ -192,6 +192,46 @@  int ll_index_to_flags(unsigned idx)
 	return im ? im->flags : -1;
 }
 
+static int ll_link_get(const char *name)
+{
+	struct {
+		struct nlmsghdr		n;
+		struct ifinfomsg	ifm;
+		char			buf[1024];
+	} req = {
+		.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg)),
+		.n.nlmsg_flags = NLM_F_REQUEST,
+		.n.nlmsg_type = RTM_GETLINK,
+	};
+	__u32 filt_mask = RTEXT_FILTER_VF | RTEXT_FILTER_SKIP_STATS;
+	struct rtnl_handle rth = {};
+	struct nlmsghdr *answer;
+	int rc = 0;
+
+	if (rtnl_open(&rth, 0) < 0)
+		return 0;
+
+	addattr32(&req.n, sizeof(req), IFLA_EXT_MASK, filt_mask);
+	addattr_l(&req.n, sizeof(req), IFLA_IFNAME, name,
+		  strlen(name) + 1);
+
+	if (rtnl_talk(&rth, &req.n, &answer) < 0)
+		goto out;
+
+	/* add entry to cache */
+	rc  = ll_remember_index(answer, NULL);
+	if (!rc) {
+		struct ifinfomsg *ifm = NLMSG_DATA(answer);
+
+		rc = ifm->ifi_index;
+	}
+
+	free(answer);
+out:
+	rtnl_close(&rth);
+	return rc;
+}
+
 unsigned ll_name_to_index(const char *name)
 {
 	const struct ll_cache *im;
@@ -204,7 +244,9 @@  unsigned ll_name_to_index(const char *name)
 	if (im)
 		return im->index;
 
-	idx = if_nametoindex(name);
+	idx = ll_link_get(name);
+	if (idx == 0)
+		idx = if_nametoindex(name);
 	if (idx == 0)
 		idx = ll_idx_a2n(name);
 	return idx;