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From: Thomas Monjalon <thomas@monjalon.net>
To: "Yang, Zhiyong" <zhiyong.yang@intel.com>
Cc: "Tan, Jianfeng" <jianfeng.tan@intel.com>,
Maxime Coquelin <maxime.coquelin@redhat.com>, "dev@dpdk.org" <dev@dpdk.org>,
"yliu@fridaylinux.org" <yliu@fridaylinux.org>, "Bie,
Tiwei" <tiwei.bie@intel.com>, "Wang, Zhihong" <zhihong.wang@intel.com>, "Wang,
Dong1" <dong1.wang@intel.com>
Date: Mon, 05 Mar 2018 09:54:55 +0100
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Subject: Re: [dpdk-dev] [PATCH 1/4] vhost: move fdset functions from
fd_man.c to fd_man.h
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05/03/2018 08:43, Yang, Zhiyong:
> From: Thomas Monjalon [mailto:thomas@monjalon.net]
> > 01/03/2018 07:02, Tan, Jianfeng:
> > > From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> > > > On 02/28/2018 02:36 AM, Yang, Zhiyong wrote:
> > > > > From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> > > > >> On 02/14/2018 03:53 PM, Zhiyong Yang wrote:
> > > > >>> lib/librte_vhost/Makefile | 3 +-
> > > > >>> lib/librte_vhost/fd_man.c | 274 -------------------------------------------
> > ---
> > > > >>> lib/librte_vhost/fd_man.h | 258
> > > > >> +++++++++++++++++++++++++++++++++++++++++--
> > > > >>> 3 files changed, 253 insertions(+), 282 deletions(-)
> > > > >>> delete mode 100644 lib/librte_vhost/fd_man.c
> > > > >>
> > > > >> I disagree with the patch.
> > > > >> It is a good thing to reuse the code, but to do it, you need to
> > > > >> extend the vhost lib API.
> > > > >>
> > > > >> New API need to be prefixed with rte_vhost_, and be declared in
> > > > >> rte_vhost.h.
> > > > >>
> > > > >> And no need to move the functions from the .c to the .h file, as
> > > > >> it
> > > > moreover
> > > > >> makes you inline them, which is not necessary here.
> > > > >
> > > > > Thanks for your reviewing the series firstly, Maxime. :)
> > > > >
> > > > > I considered to do it as you said. However I still preferred this one at last.
> > > > > Here are my reasons.
> > > > > 1) As far as I know, this set of functions are used privately in
> > > > > librte_vhost
> > > > before this feature.
> > > > > No strong request from the perspective of DPDK application. If I
> > > > understand well, It is enough to expose the functions to all PMDs
> > > > > And it is better to keep internal use in DPDK.
> > > >
> > > > But what the patch is doing is adding fd_man.h to the API, without
> > > > doing it properly. fd_man.h will be installed with other header
> > > > files, and any external application can use it.
> > > >
> > > > >
> > > > > 2) These functions help to implement vhost user, but they are not
> > > > > strongly
> > > > related to other APIs of vhost user which have already exposed.
> > > > > if we want to expose them as APIs at lib layer, many functions and
> > > > > related
> > > > data structure has to be exposed in rte_vhost.h. it looks messy.
> > > > > Your opinion?
> > > >
> > > > Yes, it is not really vhost-related, it could be part of a more
> > > > generic library. It is maybe better to duplicate these lines, or to
> > > > move this code in a existing or new library.
> > >
> > > I vote to move it to generic library, maybe eal. Poll() has better
> > compatibility even though poll() is not as performant as epoll().
> > >
> > > Thomas, how do you think?
> >
> > I don't see why it should be exported outside of DPDK, except for PMDs.
> > I would tend to keep it internal but I understand that it would mean
> > duplicating some code, which is not ideal.
> > Please could you show what would be the content of the .h in EAL?
> >
>
> If needed to expose them in eal.h,
> I think that they should be the whole fdset mechanism as followings.
>
> typedef void (*fd_cb)(int fd, void *dat, int *remove);
>
> struct fdentry {
> int fd; /* -1 indicates this entry is empty */
> fd_cb rcb; /* callback when this fd is readable. */
> fd_cb wcb; /* callback when this fd is writeable.*/
> void *dat; /* fd context */
> int busy; /* whether this entry is being used in cb. */
> };
>
> struct fdset {
> struct pollfd rwfds[MAX_FDS];
> struct fdentry fd[MAX_FDS];
> pthread_mutex_t fd_mutex;
> int num; /* current fd number of this fdset */
> };
>
> void fdset_init(struct fdset *pfdset); (not used in the patchset)
>
> int fdset_add(struct fdset *pfdset, int fd,
> fd_cb rcb, fd_cb wcb, void *dat); (used in this patchset)
>
> void *fdset_del(struct fdset *pfdset, int fd); (not used in the patchset)
>
> void *fdset_event_dispatch(void *arg); (used in this patchset)
>
> seems that we have 4 options.
> 1) expose them in librte_vhost
> 2) expose them in other existing or new libs. for example, eal.
> 3) duplicate the code lines at PMD layer.
> 4) do it as the patch does that.
It looks to be very close of the interrupt thread.
Can we have all merged in an unique event dispatcher thread?