[Qemu-devel] [PATCH v5] net: Allocating Large sized arrays to heap

[Qemu-devel] [PATCH v5] net: Allocating Large sized arrays to heap

[Pooja Dhannawat]

nc_sendv_compat has a huge stack usage of 69680 bytes approx.
Moving large arrays to heap to reduce stack usage.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Pooja Dhannawat <dhannawatpooja1@gmail.com>
---
 net/net.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/net/net.c b/net/net.c
index b0c832e..663da13 100644
--- a/net/net.c
+++ b/net/net.c
@@ -709,23 +709,28 @@ ssize_t qemu_send_packet_raw(NetClientState *nc, const uint8_t *buf, int size)
 static ssize_t nc_sendv_compat(NetClientState *nc, const struct iovec *iov,
                                int iovcnt, unsigned flags)
 {
-    uint8_t buf[NET_BUFSIZE];
+    uint8_t *buf = NULL;
     uint8_t *buffer;
     size_t offset;
+    ssize_t ret;
 
     if (iovcnt == 1) {
         buffer = iov[0].iov_base;
         offset = iov[0].iov_len;
     } else {
+        buf = g_new(uint8_t, NET_BUFSIZE);
         buffer = buf;
-        offset = iov_to_buf(iov, iovcnt, 0, buf, sizeof(buf));
+        offset = iov_to_buf(iov, iovcnt, 0, buf, NET_BUFSIZE);
     }
 
     if (flags & QEMU_NET_PACKET_FLAG_RAW && nc->info->receive_raw) {
-        return nc->info->receive_raw(nc, buffer, offset);
+        ret = nc->info->receive_raw(nc, buffer, offset);
     } else {
-        return nc->info->receive(nc, buffer, offset);
+        ret = nc->info->receive(nc, buffer, offset);
     }
+
+    g_free(buf);
+    return ret;
 }
 
 ssize_t qemu_deliver_packet_iov(NetClientState *sender,
-- 
2.5.0

Re: [Qemu-devel] [PATCH v5] net: Allocating Large sized arrays to heap

[Stefan Hajnoczi]

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On Mon, Mar 28, 2016 at 06:04:11PM +0530, Pooja Dhannawat wrote:
> nc_sendv_compat has a huge stack usage of 69680 bytes approx.
> Moving large arrays to heap to reduce stack usage.
> 
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Pooja Dhannawat <dhannawatpooja1@gmail.com>
> ---
>  net/net.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/net/net.c b/net/net.c
> index b0c832e..663da13 100644
> --- a/net/net.c
> +++ b/net/net.c
> @@ -709,23 +709,28 @@ ssize_t qemu_send_packet_raw(NetClientState *nc, const uint8_t *buf, int size)
>  static ssize_t nc_sendv_compat(NetClientState *nc, const struct iovec *iov,
>                                 int iovcnt, unsigned flags)
>  {
> -    uint8_t buf[NET_BUFSIZE];
> +    uint8_t *buf = NULL;
>      uint8_t *buffer;
>      size_t offset;
> +    ssize_t ret;
>  
>      if (iovcnt == 1) {
>          buffer = iov[0].iov_base;
>          offset = iov[0].iov_len;
>      } else {
> +        buf = g_new(uint8_t, NET_BUFSIZE);
>          buffer = buf;
> -        offset = iov_to_buf(iov, iovcnt, 0, buf, sizeof(buf));
> +        offset = iov_to_buf(iov, iovcnt, 0, buf, NET_BUFSIZE);
>      }
>  
>      if (flags & QEMU_NET_PACKET_FLAG_RAW && nc->info->receive_raw) {
> -        return nc->info->receive_raw(nc, buffer, offset);
> +        ret = nc->info->receive_raw(nc, buffer, offset);
>      } else {
> -        return nc->info->receive(nc, buffer, offset);
> +        ret = nc->info->receive(nc, buffer, offset);
>      }
> +
> +    g_free(buf);
> +    return ret;
>  }
>  
>  ssize_t qemu_deliver_packet_iov(NetClientState *sender,
> -- 
> 2.5.0

CCing Jason Wang, net subsystem maintainer.  Please use
scripts/get_maintainer.pl to find the right people to CC in future
patches.

We may also want to keep a smaller stack buffer so that reasonably-sized
packets (e.g. up to 2 KB) can be send without the performance cost of
g_malloc().

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Re: [Qemu-devel] [PATCH v5] net: Allocating Large sized arrays to heap

[Pooja Dhannawat]

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On Thu, Mar 31, 2016 at 3:28 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Mon, Mar 28, 2016 at 06:04:11PM +0530, Pooja Dhannawat wrote:
> > nc_sendv_compat has a huge stack usage of 69680 bytes approx.
> > Moving large arrays to heap to reduce stack usage.
> >
> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > Signed-off-by: Pooja Dhannawat <dhannawatpooja1@gmail.com>
> > ---
> >  net/net.c | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/net.c b/net/net.c
> > index b0c832e..663da13 100644
> > --- a/net/net.c
> > +++ b/net/net.c
> > @@ -709,23 +709,28 @@ ssize_t qemu_send_packet_raw(NetClientState *nc,
> const uint8_t *buf, int size)
> >  static ssize_t nc_sendv_compat(NetClientState *nc, const struct iovec
> *iov,
> >                                 int iovcnt, unsigned flags)
> >  {
> > -    uint8_t buf[NET_BUFSIZE];
> > +    uint8_t *buf = NULL;
> >      uint8_t *buffer;
> >      size_t offset;
> > +    ssize_t ret;
> >
> >      if (iovcnt == 1) {
> >          buffer = iov[0].iov_base;
> >          offset = iov[0].iov_len;
> >      } else {
> > +        buf = g_new(uint8_t, NET_BUFSIZE);
> >          buffer = buf;
> > -        offset = iov_to_buf(iov, iovcnt, 0, buf, sizeof(buf));
> > +        offset = iov_to_buf(iov, iovcnt, 0, buf, NET_BUFSIZE);
> >      }
> >
> >      if (flags & QEMU_NET_PACKET_FLAG_RAW && nc->info->receive_raw) {
> > -        return nc->info->receive_raw(nc, buffer, offset);
> > +        ret = nc->info->receive_raw(nc, buffer, offset);
> >      } else {
> > -        return nc->info->receive(nc, buffer, offset);
> > +        ret = nc->info->receive(nc, buffer, offset);
> >      }
> > +
> > +    g_free(buf);
> > +    return ret;
> >  }
> >
> >  ssize_t qemu_deliver_packet_iov(NetClientState *sender,
> > --
> > 2.5.0
>
> CCing Jason Wang, net subsystem maintainer.  Please use
> scripts/get_maintainer.pl to find the right people to CC in future
> patches.
>
> Yes, I am sorry about that. Fam also pointed out this thing but I forgot
this time also.
I will keep that mind from onwards.


> We may also want to keep a smaller stack buffer so that reasonably-sized
> packets (e.g. up to 2 KB) can be send without the performance cost of
> g_malloc().
>

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Re: [Qemu-devel] [PATCH v5] net: Allocating Large sized arrays to heap

[Jason Wang]

On 03/28/2016 08:34 PM, Pooja Dhannawat wrote:
> nc_sendv_compat has a huge stack usage of 69680 bytes approx.
> Moving large arrays to heap to reduce stack usage.
>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Pooja Dhannawat <dhannawatpooja1@gmail.com>
> ---
>  net/net.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/net/net.c b/net/net.c
> index b0c832e..663da13 100644
> --- a/net/net.c
> +++ b/net/net.c
> @@ -709,23 +709,28 @@ ssize_t qemu_send_packet_raw(NetClientState *nc, const uint8_t *buf, int size)
>  static ssize_t nc_sendv_compat(NetClientState *nc, const struct iovec *iov,
>                                 int iovcnt, unsigned flags)
>  {
> -    uint8_t buf[NET_BUFSIZE];
> +    uint8_t *buf = NULL;
>      uint8_t *buffer;
>      size_t offset;
> +    ssize_t ret;
>  
>      if (iovcnt == 1) {
>          buffer = iov[0].iov_base;
>          offset = iov[0].iov_len;
>      } else {
> +        buf = g_new(uint8_t, NET_BUFSIZE);
>          buffer = buf;
> -        offset = iov_to_buf(iov, iovcnt, 0, buf, sizeof(buf));
> +        offset = iov_to_buf(iov, iovcnt, 0, buf, NET_BUFSIZE);
>      }
>  
>      if (flags & QEMU_NET_PACKET_FLAG_RAW && nc->info->receive_raw) {
> -        return nc->info->receive_raw(nc, buffer, offset);
> +        ret = nc->info->receive_raw(nc, buffer, offset);
>      } else {
> -        return nc->info->receive(nc, buffer, offset);
> +        ret = nc->info->receive(nc, buffer, offset);
>      }
> +
> +    g_free(buf);
> +    return ret;
>  }
>  
>  ssize_t qemu_deliver_packet_iov(NetClientState *sender,

Applied to -net.

Thanks